of their cubes is to the cube of their difference as 61 to 1. What are the numbers ? 15. There are two numbers, which are to each other in the duplicate ratio of 4 to 3, and 24 is a mean proportional between them. What are the numbers ? INDUSTRIAL AND POLITICAL HISTORY CHAPTER XII.-ROME. For a thousand years the Romans made conquest their policy. They were essentially a martial people. Warfare, however, is destructive of the means of subsistence. While, therefore, we inquire into the industry and commerce of the Romans, with the view of ascertaining how much of our present prosperity is due to them, there is also, on the other side, the question of how much has been lost by the repression or destruction of the genius and individuality of nations of which they were guilty. The patriotic spirit which leads men to die for their country lost its force in a common subjection to Rome. The sentiment of devotion could not be strong, when the only tie uniting the provinces to the capital was that of subjugation and tribute. The fall of Rome left Europe denationalised; a spurious civilisation was followed by centuries of barbarism. tion common in the apartments of the wealthy. The exteriors of the houses were plain, but the interiors astonish us with their adornments. In one house a mosaic has been found consisting of nearly a million and a half of separate pieces in 198 squares, upon which are depicted, of the size and colours of life, twentysix horsemen and warriors, representing the battle between Alexander and Darius. Two edifices are of special interest as having belonged to the illustrious Caius Sallust and Marcus Arius Diomedes. The dwellings corresponded in their fashion and appointments to those of Rome, but did not equal the latter in their sumptuous embellishments, as we may justly infer from the difference which is known to have existed between the Pompeian baths, temples, and public buildings, and the more magnificent structures of Rome. It was a saying of Crassus that "no one was rich who could not support an army he himself was worth a million and a half sterling in landed property alone. Scaurus, the step-son of Sylla, built an amphitheatre capable of accommodating 80,000 spectators. It was supported by 360 costly marble, glass, and gilt pillars, and beautified with 3,000 statues; even by such profuse expenditures as this, he was unable to dissipate the enormous fortune bequeathed to him by his father. Though the Roman houses were comparatively small, yet the sums lavished upon their construction and furniture altogether transcend modern notions of costliness. A single table, according to Pliny, was often valued at a price exceeding that of the spoils of a city. Cæsar states that the house of Clodius the tribune cost £120,000. The suburban and country villas likewise afford examples of Roman luxury. Baths covered immense areas. Ponds for fish and eels-of which the Romans were very fond—aviaries for birds, extensive parks for game, and gardens for the choicest fruits, were regarded as necessaries. Within doors were rooms for every division of the day and every season of the year. Distaste for labour grew with the empire. While the Roman territories were small-as late, indeed, as the time of Alexander-agriculture was honoured, and the rulers of the state tilled their own lands. When the wealth of Rome increased by conquest, the cultivation of the land, and the manufactures in connection with it, were made servile occupations, so that the poor citizens who would have been skilled labourers, had there been no slaves, became state-fed paupers, ready for every political commotion. In the works of Roman writers there are allusions which prove that the Roman citizens did not despise the profits of commerce, and that where even a senator could engage, though illegally and under a feigned name, in the slave or corn traffic, or turn the skill of his slaves to account, his aversion to the occupation was overcome. Crassus and Cato in this manner gained much of their wealth. Rome, as the capital of the world, the centre of tribute flowing through a thousand channels, disposed of this revenue in a profuse and sumptuous luxury, without parallel either before or since. Denied natural resources fit for interchange, there poured in continuous streams of commodities both by land and sea, for which the tribute from the provinces and the plunder accruing from conquest afforded exhaustless means of payment. While the Roman citizens thus consumed the material wealth brought to their city, foreign merchants made it a cosmopolitan martingales were destroyed for their brains alone. Vitellius and or clearing-house for a fresh dispersion of the products of the Alexandrian trade, the traffic with China and India, the Scythian fur trade, and the trade with Africa, Spain, and Gaul. The productions of every clime were thus brought to the imperial centre, and the merchants enjoyed the advantages of universal commerce, without the cost and time of extensive travel. Amongst the middle classes, in the early age of simple wants, a merchant's guild was instituted, which enlarged its operations as time went on, but was not held in honour. The fruit and corn dealers took a prominent place in the home trade. Tanners and cordwainers were the most thriving handicraftsmen. Weaving and dyeing were subsequently added to the limited list of manufacturing industries. The facilities afforded at Rome for interchange were purely political. The revenue that poured into its treasury was prodigious. The private fortunes of some of its citizens exceeded the whole wealth of many modern kingdoms. The capital was never anything else than a depôt, importing everything, and exporting no produce of its own. Thus corn arrived from Sicily, Sardinia, and Egypt; amber from the Baltic; fine cloths from Malta and Mauritania; silks, spices, and gems by caravan from the Indies. The produce of the soil, the mines and the industry of every province, as well as costly works of taste or genius, were at the command of a prodigal aristocracy and wealthy citizens, of victorious generals and of provincial governors, who returned to squander at Rome the treasures they had amassed by official avarice and This profusion was copied in other cities. The disinterment of Pompeii and Herculaneum from their graves of Vesuvian ashes and lava has disclosed the splendid decora extortion. Voluptuousness culminated during the time of the emperors. To the taste for profusion was added that for the rare delicacies of the table. Pyramids of fowl and game, Trojan horses (i.e., wild boars filled with a variety of small game), peacocks, cranes, and nightingales, appeared at the dinners of the great. "If a man will eat daintily," a writer of the period observes, "he must indulge in Samian peacocks, Phrygian fowls, Melian cranes, Ætolian kids, Chalcedonian porpoises, Tarentine oysters, Chian mussels, Egyptian dates, Spanish acorns, murenæ or seaeels from Tarshish, pikes from Pessinus, sea-fish from Rhodes." Mark Antony served up eight whole boars to twelve guests. Caligula wantonly dissolved priceless pearls in vinegar as part of the fare at his feasts. Thousands of peacocks and nightHeliogabalus are to this day held up as the types of gluttony. Lucullus, a more refined epicure, dedicated his saloons to certain gods, and affixed a scale of entertainment to each apartment. When acting as the host of his friends, Pompey and Cæsar, he directed his servants to furnish an extemporaneous supper in the room Apollo, and explained to his guests, when they were astonished at its magnificence, that it was the rule of his house to spend £1,250 upon every banquet in that apartment. The extravagance in dress corresponded with that in eating. Lucullus lent a hundred purple robes, and offered two hundred to one who wanted them for the actors in some public games. It is related of the Roman Apicius, that when, by senseless extravagance at table, he had reduced his patrimony to the last hundred thousand pounds, he put an end to his life, as the only means of escaping destitution. Caesar, when starting to administer the government of Spain, was arrested by his creditors for a debt of a million and a half sterling; nor would they allow him to set out till Crassus became his surety. A short tenure of office, however, enabled Cæsar not only to pay his debts, but to use a still larger sum in purchasing popularity at Rome. Mark Antony out-distanced all these examples. In a few years of his administration of the states of Asia Minor it is said that he appropriated about forty millions sterling of taxes, and then made the people pay the same amount as before twice a year instead of once. Courage could co-exist with commerce, for Tyre withstood Nebuchadnezzar for thirteen years, and New Tyre Alexander for seven months, while Rome was a century in subduing Carthage. Roman domination was unfavourable to commerce: the productive resources of the earth declined as it became Romanised. The Romans were, however, too sagacious to rest satisfied with barren conquests. Though unwilling to labour, they stimulated industry to a certain degree in every country that came under their sway. They removed the sense of subjugation by enrolling the conquered people as part and parcel of the empire. They made roads and bridges, they built cities and aqueducts, and brought the soil into cultivation. They encouraged the arts and sciences of the Greeks, and extended their own civilisation to many other countries. The Romans, likewise, in obtaining the supremacy of the world, put an end to the incessant petty warfare between rival states, and established an unrestricted trade and a community of interests in all their provinces. Their chief service to commerce was that of rendering intercommunication everywhere easy and safe. Their great works in road-making spread over every province, from Britain to the Euphrates. So broad and solid were many of these roads that parts still remain entire. Watling Street in our own country is an example. This road led from the Kentish coast through London to Carnarvon, and is still one of the best English roads. After good roads followed the system of posts or stages, by which couriers in the service of the emperors could change horses-a plan said to have been first used by Cyrus. The posts only conveyed public despatches. Post-offices, as we understand them, are quite of modern origin, Louis XI. having introduced them into France, and Charles II. into England. Our monetary and banking systems have both been founded on Roman practices. The £ s. d. of accounts are the initials of libræ, solidi, and denarii-Latin terms applied to the metals used as media of exchange, whether by weight or coinage. There were in Rome government banks, private banks, and loan banks. A prevalent prejudice against receiving interest for money lent caused the private bankers to be but little esteemed; but the government banks were managed by men of high position. Loan banks lent money on land and other property, for a certain term, without interest. The Romans also (some say the Rhodians) introduced underwriting or marine insurance. The downfall of the Western Empire marks an epoch in political and commercial history. The relation between the different nations entirely changed at this period. It is the historian's line of demarcation between ancient history and that of the Middle Ages. following the irruptions of the Goths and Huns, by whom industry and trade were regarded as effeminate. For centuries distinction amongst the great was measured by landed possessions and the number of vassals. War was the only means of increasing property, and bands of idle retainers were kept, ever ready to obey the behests of their chief. The Byzantine empire at this epoch bridged over the interval between the past and the future. Constantinople, free from the Scythian hordes, which had darkened Europe, retained many of the traditions of Rome, and kept up a commercial intercourse with the countries of the East. It was mainly by its instrumentality that the restoration of art and science was effected. Italy was the first to exhibit the growth of new tastes, which, as they spread through Europe, changed the aspect of social life. The nobles, diverted from fighting, displayed their wealth in dress and equipage. Their retainers gradually became peace. able labourers and handicraftsmen, and their descendants have placed within the reach of the poor of modern times many things either unobtainable, or obtainable only with great cost and difficulty even by the Emperors of Rome. There were not wanting rulers who viewed the revival of commerce with alarm, and who enacted sumptuary laws, copied from those of Rome, concerning the number of guests, the variety of viands, and the cost of entertainments. Even in our own country, for instance (1377), only two courses, and two kinds of food at each course, were permitted by law, except at festivals. Furs and silks were prohibited to any one with an income of less than £100 a-year. Foreign cloth was to be worn only by members of the royal family. Henry IV. restricted the breadth of the toes of shoes to six inches. Edward IV. commanded that only lords should wear a short mantle. An edict against gilt spurs and bridles was issued in Ireland (1447); and any one was empowered to seize and keep for his own use horses caparisoned contrary to law. Such measures are always impolitic and radically bad. Where people are inclined to extravagance, sumptuary laws are powerless to check it, and they are met by bad habits and evasion-they cannot alter dispositions. It was in the reign of Justinian (527-565) that industry and commerce received from a foreign source an impulse, the inflaence of which has spread more and more in succeeding ages. This was the introduction of the silkworm. For many centuries silk was thought to be a vegetable down, like cotton, its true origin having been jealously concealed from merchants. Two missionaries returning from China concealed in a cane some silkworms' eggs, which they brought to Constantinople. Worms CHAPTER XIII. THE NATIONS OF THE MIDDLE AGES, from these eggs were distributed throughout the Byzantine FROM B.C. 476 TO A.D. 1453. COMMERCIAL RELATIONS OF THE BYZANTINE OR EASTERN ROMAN EMPIRE. SEATED upon two continents, on each side of the narrow strait between the Euxine and the Mediterranean, Constantinople has an unrivalled position. Its site was selected by the Greek colonisers with a sagacity to which, as Hallam observes, the course of events has given the appearance of prescience. Under the name of Byzantium, the city flourished for a thousand years (B.C. 658 to A.D. 330). It was alternately held during the Peloponnesian wars by the Athenians and Lacedæmonians, and after the expulsion of the latter (B.c. 390) by Thrasybulus, it remained for some time independent. The Macedonians were afterwards masters of the city. Severus (A.D. 196) took it after a three years' siege, and razed a large part of it to the ground. Constantine (A.D. 330) rebuilt it, called it after his own name, and removed thither the seat of empire from Rome. But the Eternal City could not be thus easily stripped of its metropolitan rank. The removal of the capital led ere long to the division of the Roman world into Eastern and Western Empires. Constantinople became the centre of a power Greek in character, Roman in name. We have seen how, after the conquest of Greece, Egypt, and the East, Rome was flooded with ill-gotten wealth. The citizens made display the chief aim of existence; wealth became mere tinsel, and outward prosperity a hollow mask. At length, Western and Southern Europe were overrun by tribes of barbarians, who trampled in the dust the glitter of Rome, and with it destroyed the previous geographical knowledge arising out of the world's commerce. The feudal system had its origin in the period of anarchy empire. Cyprus and Sicily soon produced great numbers, and the Peloponnesus became known as the Morea, from the white mulberry trees, which began to be abundantly cultivated there. The early Byzantine trade with India was carried on through Egypt, the Persians at that time intercepting the direct overland traffic. Soon after, the Euphrates valley was once more opened to caravans. Syria and Mesopotamia were subdued by the Caliph Omar, who built the town of Bassora; yet few goods reached Constantinople, for the empire was nearly always at war with the Arabs. When Alexandria fell into the hands of the latter, the communication by way of Egypt was cut off, as the Christian states would enter into no dealings with the infidels. Such, however, was the desire for Indian commodities, that a route was opened by way of the Greek settlements on the Black Sea and Independent Tartary; and for 200 years the products of India and China reached Constantinople almost exclusively by this circuitous course. Each generation improved the commerce of the Mediterranean coasts, and an active trade arose between the Greek empire and Spain, Africa, and the Republics of Italy. Amongst the commodities from the East and the West, which passed through Constantinople, and showed the extent of Byzantine commerce during Justinian's reign, were Egyptian silks and half silks, raw silks, linen, and flax; sweet wines and fruits-especially dates and figs-sugar, cassia, and drugs: Indian spices, cloves, nutmegs, mace, cinnamon, galanga root, and large quantities of pepper. Precious stones, perfumes, and horses also came from India. Silver was imported by the Genoese, probably from Spain; while the Pisanese introduced woollen stuffs, scarlet, and fustian. Few of the exports were native produce, for Constantinople was an emporium rather than a manufacturing city. Grecian velvets, other silk stuffs, cotton cloths, linen, and wool; nuts, saffron, oil, timber, pitch, honey; gold, silver, mercury, copper, iron, tin, lead, weapons, and slaves are enumerated. Restrictive laws led to an illicit trade in some varieties of goods, of which purple state robes were an example, their export being prohibited. The commercial vigour of the ancient Greeks never distinguished their Byzantine posterity. The land trade of Constantinople was carried on with no great activity. A military people called the Avars, inhabiting the provinces of the Danube lying between the Greek empire and Germany, had, up to the ninth century, the management of the Western land traffic. They were the carriers of goods, some of which eventually reached the most northern kingdoms of Europe. The wealth accruing from this trade enervated these Avars. It made them "refined barbarians," but could not save them from the inroads of a hardier tribe, like themselves of Slavonian origin, and known as Bulgarians. For two centuries the Bulgarians carried on the trade between Constantinople and Germany, till disputes arose between them and the Greeks, who were at first defeated in the fierce encounters that ensued; but the Bulgarians were at length subdued by the Emperor Basil in 1018. The Bulgarians had probably been driven to invade the Greek territory by the advance of the Ungrians and Magyars, who in the tenth century took possession of the plain of the Danube, and established there a kingdom, which still preserves in its name (Hungary) and that of its people (Magyars) the memory of its founders. The Ungrians made Semlin in Hungary the depôt of the international transport trade. They took upon themselves the conduct of the traffic throughout, built factories, and established agencies in the capital, where Stephen I., who died in 1038, erected for their encouragement a splendid place of worship. Hungary flourished in every town because of the rich profits of their extensive business as carriers and brokers. The Western land traffic waned, and in the end disappeared, before the rising maritime commerce of Venice, Genoa, and other Italian republics. The commodities which specially distinguished the Western trade consisted of raw produce, manufactures, and works of art; Greek artistic work; olives, saffron, and hazel nuts; oil, liquorice, raw silk, silk and mixed stuffs; purple and priestly robes; gold dust and Eastern spices; pepper, ginger, cloves, nutmegs, galanga root, and anise-seed. Sword belts bound with brass and copper were sent by sea to the West, and in the land traffic Constantinople received overland from Germany Wendish slaves or serfs; from Bohemia and Moravia, weapons of ancient German manufacture; wooden tools and saddles from the Low Countries; woollen and linen, principally of Friesland make, and metals, from Transylvania and Hungary. During a part only of this period could Byzantine commerce take the old Chaldean road to India. Obstructed by Persia and by continual contentions with the Arabs from employing it, the route through Independent Tartary was made use of. By zantine commerce both by land and sea at length lost all its importance, and fell almost entirely into the hands of the Italians. In our last lesson we learnt that sound was produced when the air was set in vibration by a sonorous body. If in any way we can cause a succession of gentle taps to succeed one another with sufficient rapidity, we shall find that they lose their individuality, and merge into a continuous note. An easy way of obtaining experimental illustration of this consists in holding a piece of card against the teeth of a rapidly revolving wheel. The separate taps produced as each cog strikes it will not be distinguishable, but will coalesce to form a clear and distinct note, the pitch of which becomes higher and higher as the wheel rotates more rapidly. In this manner we may measure the number of vibrations per second required to produce any given note, a number which will always be found uniform. Savart's toothed wheel (Fig. 6) is an apparatus devised for this purpose. It consists of two wheels, A and B, mounted in a strong wooden frame-work. The larger of these, A, is fitted with a handle by which to turn it, and a strap passing over its own circumference and also over a pulley on the axle of the toothed wheel, B, causes the latter to rotate with considerable velocity. A piece of card is fixed to the plate E in such a way that the teeth of the wheel may catch against it and set it in rapid vibration, the rapidity of the pulsations being determined by the rate at which the teeth strike against it. To the axis of this wheel there is fixed an indicator, H, which shows the number of revolutions it makes, and, multiplying this by the number of teeth, we learn the number of vibrations. The best way of using the instrument is, when a steady note is being produced, to allow it to continue for several seconds, and then divide the number of vibrations made by the card by the number of seconds. We thus ascertain the number of vibrations per second required to produce the sound. To produce the note an octave higher, we must just double this number. It is important for us to remember that when we speak here of a vibration, we mean the oscillation of the vibrating particles to and fro, that is, its complete double motion. In France, each single oscillation to or fro is counted, and hence twice the number of vibrations are said to be required to produce any note. If this distinction be clearly borne in mind, little inconvenience will be caused by the different modes of speaking of the same thing. The question now suggests itself, how many vibrations pe. second are requisite in order to produce a distinct musical sound. To this we cannot give a decided answer, since different ears are found to vary considerably in their power of appreciating sounds. To ascertain the limit, Savart slightly modified his apparatus, removing the toothed wheel, and substituting for it an iron bar, which passed between two thin wooden plates, so placed as almost to touch it. When the bar passed between them, a grave sound was produced by the displacement of the air, and he imagined that a distinct but very deep sound could be perceived when the number of these pulsations was about 12 or 14 per second. Other observers have placed the number as high as 32, while some place it as low as 8. The upper limit to the number of vibrations that can be heard also varies very considerably. It depends partly upon the intensity of the vibrations and their amplitude. Some place the limit at from 20,000 to 24,000 vibrations per second; there seems, however, little doubt that a sound corresponding to 38,000 vibrations is audible in most ears. By experimenting with very acute sounds, Dr. Wollaston found that the limits of hearing in different people varied greatly. He sounded a series of small pipes in succession, before a number of people, and found that frequently the ascent of a single note produced to some the change from sound to complete silence; and while some experienced a sound of penetrating shrillness, others were quite unconscious of any sound whatever. There are in Nature sounds so shrill that they are beyond the hearing of many people; thus, for instance, the needle-like cries of the bat are unheard by many; some, too, fail to hear the chirp of the cricket. We may say, then, that sounds which the ear can distinguish range between 14 and 40,000 vibrations per second. The practical range of musical sounds is, however, much more limited. The deepest sound produced by any musical instrument appears to require about 28 vibrations, and the highest note, which is probably the upper D of the piccolo flute, requires 4,752 vibrations. For ordinary purposes, however, the range is from 40 to 4,000 vibrations, that is, a compass of about seven octaves. There are several other ways in which we may cause a regular series of pulsations to produce a musical note. If we can interrupt a stream of air sufficiently often, we shall produce a series of puffs, which will combine into a tone. This can be easily effected by taking a circular sheet of tin, or millboard, and puncturing a series of holes in a circle round its centre (Fig. 7). Fix the disc to a whirling table, or cause it, by means of a multiplying wheel, to revolve rapidly. Then take a blowpipe or a piece of india-rubber tubing with a jet at the end, and holding the jet opposite to the line of the openings blow through it; the current will be interrupted when the card is against the jet, but will pass whenever an aperture comes opposite it. In this way the current will be frequently interrupted, and a musical note will be produced, the pitch of which becomes higher and higher as the disc is made to rotate more rapidly. Now let us look at the recording portion of the apparatus. On the upper end of the spindle T there is cut a screw, which works in the teeth of the wheels that carry the hands. As the spindle turns, these wheels are moved by it, each revolution causing the wheel P to advance one tooth. The second wheel makes one revolution for every 100 made by the other. By pressing the stud, D, on the right-hand side of the instrument, the wheels are removed from the screw, on the upper part of the spindle, T, and thus cease to record; on pressing C, on the left-hand side of the instrument, contact is again renewed, and thus we can let the wheels remain in action as long as we like. An illustration of the manner of using the apparatus will make this quite clear to the reader (Fig. 11). We will suppose that we have a tuning-fork, and want to ascertain the number of vibrations it produces in the course of a second. We place Fig. 10. If we construct a disc with several concentric rings, having varying numbers of apertures, we shall be able to produce different sounds according to which part we hold the jet against. It is somewhat difficult to ascertain by this arrangement the exact number of interruptions per second; an apparatus was, however, devised by an eminent French natural philosopher, Cagniard de la Tour, which serves to register them very accurately. This curious acoustic instrument, which was called by him the Sirène, or Siren, because of its power of emitting sounds under water, is represented in Figs. 8 and 9 in the annexed illustration, the former showing the instrument complete, and the latter a view of a vertical section of it. The wheel-work at the upper part of the siren is for the purpose of recording the revolutions of the disc, but we will turn our attention to the other part first. o is a brass cylinder into which air is driven from the acoustic bellows, E, arrangements being made by which the power of the blast can be modified at pleasure. The upper end of o is closed by a plate, B, of brass or copper, perforated with twenty holes, arranged in a circle as shown in Fig. 10; through these apertures the air escapes. We want now some means of interrupting the current from these so as to produce a series of puffs instead of a continuous stream.. This is accomplished by another disc, A, similar to that which closes o; this disc is mounted on a spindle, T, the ends of which are pointed so as to turn with as little friction as possible. A small depression is made in the centre of B to carry the lower end of this, and the upper end turns in a cavity in the end of the screw on the top of the instrument. The whole is very carefully constructed, so that friction is reduced to a minimum. The number of apertures in each disc is precisely the same, and they correspond in position, so that all the openings are opened or closed simultaneously. Only one puff is, therefore, produced by the twenty holes; the sound is, however, much more powerful than if there were only one aperture. Now it will be seen that for every revolution A makes, 20 distinct pulsations will be produced in the air, and we therefore only need some means of causing this disc to revolve rapidly, and of recording its revolutions. The former of these is easily accomplished. The openings in B, instead of being at right angles to the plane of the disc, are slightly inclined, as at m (Fig. 10), so that the air issues in currents directed to one side. The rotating disc, A, has its apertures inclined slightly in the other direction, as at n, and thus it will be seen that the air as it issues strikes against the sides of these apertures, and sets the disc in rotation. The force produced in this way is but small, but as the disc turns very easily, it is quite sufficient, and by merely increasing the pressure of the air from the bellows, we can raise the pitch of the note as high as we desire. m B Fig. 11. the siren in the wind. chest of the bellows, and cause it to sound, having first thrown the wheelD work out of gear; we then excite the tuning. fork by striking it or by drawing a violin-bow across it. The occur rence of beats in the sound will show us that the two notes are not in unison; we therefore adjust the force of the bellows till the beats. gradually become slower and slower, and at last vanish, showing that now the siren and the fork are producing the same note. Keeping the pressure uniform, so that the same note continues to be uttered, we press C, and holding a watch in the hand, allow the wheels to record the revolutions for a given period, say, exactly one minute. At the expira tion of this time we press the stud D, and having thus stopped the wheelwork, read off the number of revolutions indicated. Suppose we find the revolutions recorded to be 768, then, since at every revolution the current of air is interrupted 20 times, we must clearly have produced 768 x 20, or 15,360 vibrations in the 60 seconds. Dividing this by 60, we obtain the quotient 256, which is the number of vibrations per second produced by the fork. The note is that generally known as middle C. It has been noticed of late years that the pitch of the tuningfork has been gradually getting higher, and, which is of more importance, that it differs considerably in different cities and countries. This is productive of some inconvenience, and in France a commission was appointed some ten or twelve years ago to inquire into the subject. After comparing the different standards, they recommended the adoption in France of a normal diapason. A standard tuning-fork was prepared in accordance with their recommendation. The fork, which gives the sound of the first A in the treble, produces 435 complete vibrations in the second. On this scale middle C requires 261, and the pitch is therefore slightly higher than the English. There being, however, no fixed standard in England. different makers vary slightly, and hence there is a want of that unifor mity which is desirable. LESSONS IN GEOLOGY.-XXVI. PLIOCENE AND PLEISTOCENE PERIODS. In the fossils yielded by the deposits of this period, more than one-half are found to be recent or existing species. The Pliocene period is but meagrely represented in England. In the counties of Suffolk and Essex are found beds of soft marly sands belonging to this age, containing large numbers of shells, reaching the thickness of some fifty or sixty feet. They have acquired the provincial name of "crag," and are used by the farmers to fertilise those heavy soils which are deficient in calcareous matter. On the Continent the Pliocene deposits attain a great magnitude. The Subapennine hills of Italy are accumulations of these beds, reaching a thickness of 2,000 feet; and in the east of Europe, to the north of the Black Sea, and stretching round the Caspian and Sea of Aral, is a widely-extended Plio cene area. In England the Pliocene beds are divided into two 1. The White or Coralline Crag. 2. The Red Crag. The Coralline crag was the first formed. It only extends in a narrow belt for about twenty miles between the rivers Alde and Stour. It consists of a mass of broken shells and corals, which occasionally agglomerates into a soft building stone. Although called coralline crag, corals (as they are now defined) are not frequently found in it. The great mass of the fossils are bryozoa, or rather bryozoaria-that is, structures built up by colonies of bryozoa. The term bryozoa (animal moss) was first used by Ehrenberg to denote those zoophytes of which the Flustra and Eschara are examples. These differ from the coral zoophytes in having two openings to the digestive sac instead of one. In Fig. 154 we give a specimen of a bryozoaria, the Fascicularia aurantium. Each of the little punctures over the surface was the home or cell of a bryozoum. Probably by means of tentacles the animal caused a current of water to pass into its sac, and here not only was all the organic matter upon which it existed abstracted from the water, but also the lime 161 154 The Norwich crag, which is sometimes called the Mammaliferous crag, because of the number of mammal remains which it contains, is found in the neighbourhood of Norwich. Its shells are much more recent than the Coralline crags, and more northern than those of the Red crag. Near Bridlington, on the coast of Yorkshire, is another deposit of a similar age. These and the Forest-bed are sometimes classed under the Post-pliocene. The Forest bed occupies near Cromer the position of the Norwich crag. It is an ancient forest which was submerged beneath the sea-level, and then sands and clays were deposited upon it. The forest has been traced forty miles. The stumps of the trees are still in their upright positions: they are Scotch firs, yew, sloe, alder, and oak. These beds contain the remains of the elephant, mammoth, rhinoceros, hippopotamus, beaver, bear, deer, and other mammals. 158 164 160 165 155 which the water held in solution by virtue of the presence of carbonic acid gas, and with the lime the zoophyte added something to the structure which was the common work of the colony. The section we give shows how the work increased from a point one generation building upon the cells in which their fathers lived and died. The same process is in operation to-day on the coral-reefs. The prolific growth of the echini, the presence of bryozoa, and the evidences we have of the existence of a multitude of testacea, prove that the Coralline crag must have been deposited in the tranquil waters of a deep sea. The temperature did not reach extremes, and was not tropical, for we find one of the most characteristic of the Coralline crag shells is the Astarte Omalii, which is a Northern form (Fig. 155). The Red crag was probably formed when the sea was more shallow, and when the climate began to change prior to the setting in of the Glacial period, when an Arctic cold extended over Europe. Remains of the mastodon have been yielded by the crag, and some of the more prominent of its fossils are Temnechinus excavatus (Fig. 156), Terebratula grandis (Fig. 157), Cardita senilis (Fig. 158), Voluta Lamberti (Fig. 159). VOL. VI. 162 159 THE PLEISTOCENE PERIOD, or, as it is now generally called, the Post-pliocene, is the uppermost, and one of the most interesting of the stratified deposits. The Northern Drift. - In those countries which lie north of latitude 50° is found a most peculiar deposit. It has received various names-Northern drift, Diluvium, Boulder clay, Glacial deposits and it is known in Scotland as Till. It is a heap of débris of sand and clay, sometimes stratifiedmore often not-mixed with angular fragments of the rock of the neighbourhood. Sometimes these fragments are actually polished on one side, and the flat surface exhibits parallel 163 scratches. Whenever the drift rests directly on hard rock, such as granite, the face of the rock is found smoothed and striated similarly to the fragments. Moreover, in many parts of the British Isles the rocks of a valley are found smoothed and scratched. Take for example the neighbourhood of Snowdon. Six valleys radiate from the apex of the mountain, and in each of these valleys the rocks are all smoothed, and those which protrude above the surface of the ground near the bottom of the valleys are rounded. The scratchings are always parallel to the direction of the valley, and have evidently been made by some hard substance which filled the valley being dragged forcibly through it, a process which must have frequently been repeated, for one set of scratches may often be seen covering another older set, which have another inclination, or are not quite parallel to the new ones. These appearances were attempted to be explained by those who called the drift Diluvium, upon the supposition that they were the effects of the Flood; that when the "fountains of the great deep were broken up," surges of water rushed over the surface of the land, leaving heaps of gravel, and hurrying masses of rock through the valleys, scratching their sides. Scattered But this explanation is evidently unsatisfactory; moreover, it is quite incapable of accounting for erratic blocks. over the country are blocks of rock-they are of all sizes, all shapes, and are found in all positions. They are generally not of the same kind as the rock of the country, but have, by some means or other, been transported many miles. Blocks of granite and gneiss from the Highlands are found fifty or sixty miles south. The " "boulders," as they are called, which strew Lancashire, Cheshire, Shropshire, and Staffordshire, evidently 144 |