causes are alleged for the change: (1) deterioration in the value of the refuse, owing to the diminished use of wood as fuel, and increased use of coal and coke for houses and factories, and (2) increased distance of farms from the city, owing to the increase of suburban villas.

Trees in Streets and Squares.— Of these there are now about 90,000, besides 20,000 in the cemeteries. The roots of the trees planted in the streets and squares have a network of small drains for the supply of moisture. These are con

ing stones have been the subject of care- cient to cover 82,000 square yards, or ful inquiry and experiment, and the size say 2,343 yards per cart load. I do not finally adopted has a surface of 6 inches consider the hose system suitable for by 4 inches, and a depth of 64 inches. On adoption here, except in the case of steep gradients larger stones are used. steep gradients like High Street and the Formerly the size was 9 inches each way. Bull Ring, where a horse would work These stones were found to get rounded with difficulty. Since 1873 the house at the edges and corners, and to present refuse has had to to be placed each an uneven surface. The steam rolling of night in convenient boxes, in front of the macadamised streets is done by con- the houses, the contractor's carts calling tract, the cost being but little less than for and removing the same early in the horse rolling. The asphalte carriage morning. The removal of this house ways are bedded on beton 4 inches thick, refuse costs the city £80,000 per annum; well pressed down (in very wet weather formerly it was a source of income to bitumen is used instead, as the beton the amount of £20,000 per annum. Two does not set quickly), over the beton a layer of mortar, and then, at the end of five days a layer of asphalt 1 inch thick. The annual cost of footpaths of all kinds within the city is £43,600. The cleansing and flushing of streets and removal of house refuse costs annually £160,000. Each ward has its own set of sweepers, &c. Since 1873 a special tax has been levied for sweeping footpaths; previously each householder had to do that duty. There are in all 3,120 men and women employed in sweeping the streets and removing refuse. The street watering nected by a central drain, having a valve, on paved streets is done from April 15 and leading to the main sewer. The to September 30; on others from March average cost of a tree, including trans15 to October 15. About 22 per cent. of planting, propping, draining, grid, &c., the area of the streets is watered by is £7, and about 90 per cent. of the jointed pipes, and the rest by watering transplanted trees succeed. There are carts. The first mode is stated to cost only about half as much, area for area, as the second mode, but then the amount paid for horse hire is nearly double that in Birmingham. The watering carts belong to the municipality; the horses belong to contractors. The hydrants used for street watering are about 40 yards apart; the jointed pipes by which the water is distributed are 1 inch in diameter, in seven lengths of 8 feet each, on wheels, the joints being made with gutta-percha, the man with his finger on the nozzle regulating the quantity of water put on. We found in the Rue Castiglione, the carriageway whereof is 22 yards wide, that it took the man, on an average, thirteen minutes to water only 33 yards in length of carriageway, and as each length is watered he uses a broom to sweep up the horse dung, &c. With one of our horses and carts a man can put on thirty-five loads, of 330 gallons each per day, and this quantity is suffiYou XXIV.-No. 4-21.

three nurseries for trees, with an area of 6 acres. The qualities sought in such trees are (a) rapid growth, (b) shade, (c) non-liability to attack by insects; and the trees selected on these grounds are chestnut, elm, the western plane, lime, and maple. 115 men are employed attending to the trees. The seats in streets and squares number 300.

Sewage.-We visited the great sewer in the Rue de la Pépinière, being met there by the officers of the municipality, detailed by order of M. Bufflers. This sewer was lighted up by means of fiftysix moderator lamps. The man in at tendance showed the apparatus for pushing along sand and mud deposited on the bottom of the sewer. The sewer first inspected was of the second class. The water pipes and gas pipes are attached to the crown or sides of the sewers, thus avoiding tearing up the roadway when pipes need repairing. A truck, with paddle board moved by the

current, is used to force along the sand plain has increased on an average 450 and mud. We next visited the main per cent., and in one case 4,000 per cent., sewer, or collector of all sewage coming or a forty-fold increase. The plain confrom the right bank of the Seine. The tains 3,000 acres, of which 1,075 are mean velocity in the collector was 165 feet per minute. The sewers receive (1) large portions of street sweepings; (2) storm water; (3) water thrown out from houses; (4) contents of water closets; (5) urine from closets fitted with double cylinder. From 500 to 600 men are employed in the sewers, of whom 32 work in the great collector. The length of this main sewer is 7 miles, the length of main on the left bank of river is 5 miles, and the total length of sewers in the city is 500 miles. The daily outfall of all sewers is 300,000 cubic meters, or 66,000,000 gallons.

treated with sewage. The main pipes are of beton, varying from 2 ft. to 4 ft. diameter; the smaller are of Doulton's glazed earthenware. Nine miles further from the city is a suitable tract of land, near St. Germains, with an area of 3,750 acres, and the city is in treaty with the State for its permanent acquisition. If successful, it is intended to turn all the sewage on to these two plains. We saw on the sewage farm all kinds of flowers, fruit, vegetables and trees suitable to the climate; the crops appeared healthy and abundant; the water that had passed through the soil seemed quite clean, and was tasteless. The drain pipes for collecting this filtered water are 6,600 ft. in length, the upper half, 3,300 ft., having holes; the lower part next the outfall being quite closed. The results of experiment so far, in yield, per acre, are: Artichokes, 20,000 to 30,000 heads; califlowers, 12,000 heads, weighing 16 tons; carrots, 32 to 52 tons; celery, over 40 tons; cabbage, 56 tons; onions, 24 to 32

Cesspools. Of these there are still in Paris about 240,000. In the new districts the double cylinder is used; the inner cylinder is pierced with holes to allow of the escape of liquid matter into the outer cylinder, and thence to the sewer. The solid matter is carried away in closed carts and dried at Bondy, and sold for manure. It retains but oneeighth of the nitrogenous elements, and is of little value as manure. The com- tons; potatoes, 12 to 16 tons; pumppany that undertakes this work receives a yearly grant in aid.

kins, 48 to 56 tons. About 10,000 cabbages are planted to the acre, and of Sewage Farms at Gennevilliers.· these about two-thirds succeed. More We visited the works at Asnieres, five than a million heads of cabbages are miles below the city, being met by MM. taken from the plain every year, each Bufflers and Durand-Claye. A centrifu- weighing on the average 11 lbs., or in all gal pump, worked by a 400 horse-power nearly 5,000 tons. It was stated that Corliss engine, lifts in a day about there was no bad taste or smell in the 13,200,000 gallons of sewage (one-fifth plants so long as only the roots were in of the total amount) to a height of 39 contact with the sewage, and that the feet, into pipes which carry it across the plants best suited to sewage treatment Seine to the formerly arid chalky plain are green succulent ones. Young trees of Gennevilliers (a distance of about thrive remarkably well. The experiment 6,600 feet) for distribution by means of has shown that trees well nourished when open channels over the fields and gar- young thrive best ultimately, even if redens. The tube is 3 ft. 7 in. in diame- moved to a poorer soil. To trees the ter. The supply ceases when desired by sewage supply must be stopped at the the farmers. Besides this amount there end of the summer. Mint and other are about 8,500,000 gallons daily received plants, are cultivated for perfumes and on another part of this plain from St. for flavoring, and succeed remarkably Ouen, from which it flows without pump- well. Experiments extended over nine ing. The remainder of the city sewage years show that on such soil as the plain is thrown direct into the Seine, causing of Gennevilliers, about 3,960,000 per a horrible stench for miles. The present acre per annum is the quantity that can pumping works have cost £120,000; the be most effectively utilized. At this rate proposed further expenditure is £400,000. about 5,500 acres would suffice for the These works have been seven years in sewage of the city with its 2,000,000 of operation; the value of the land on the people. The sewage is now given gratis,

but it is proposed to make a small charge the sewage should be by open furrows, as to prevent abuses. A Commission of at Gennevilliers. (3) That the supply Inquiry has just reported, and its conclu- should be intermittent and frequent. (4) sions may be summarized (1) Green That sewage be not allowed to touch any plants, cabbage, celery, lettuce, root part of the plant except the root. (5) crops, and "industrial plants," such as That the place of the furrows should be mint, are those best adapted to sewage frequently changed. treatment. (2) That the distribution of

THE RELATION BETWEEN ELECTRICITY AND LIGHT.*

From 44 Nature."

Prof. Aryton knows this perfectly well; phragms. The water cannot move withit is merely a question of words, i. e., of out straining and bending these diawhat you understand by the word electricity.

I want you, then, to regard this battery and all electrical machines and batteries as kinds of electricity pumps, which drive the electricity along through the wire very much as a water pump can drive water along pipes. While this is going on the wire manifests a whole series of properties, which are called the properties of the current.

phragms, and if you allow it, these strained partitions will recover themselves and drive the water back again. [Here was explained the process of charging a Leyden jar.] The essential thing to remember is that we may have electrical energy in two forms, the static and the kinetic; and it is, therefore, also possible to have the rapid alternation from one of these forms to the other, called vibration.

[Here were shown an ignited platinum Now we will pass to the second queswire, the electric arc between to carbons, tion: What do you mean by light? an electric machine spark, an induction And the first and obvious answer is, coil spark, and a vacuum tube glow. Also everybody knows. And everybody that a large nail was magnetized by being is not blind does know to a certain exwrapped in the current, and two helices tent. We have a special sense-organ for were suspended and seen to direct and appreciating light, whereas we have none attract each other.] for electricity. Nevertheless, we must To make a magnet, then, we only need admit that we really know very little a current of electricity flowing round about the intimate nature of light-very and round in a whirl. A vortex or little more than about electricity. But whirlpool of electricity is, in fact, a we do know this, that light is a form of magnet; and vice versa. And these energy; and, morever, that it is energy whirls have the power of directing and rapidly alternating between the static attracting other previously existing and the kinetic forms-that it is, in fact, whirls according to certain laws, called a special kind of energy of vibration. the laws of magnetism. And, moreover, We are absolutely certain that light is a they have the power of exciting fresh periodic disturbance in some medium, whirls in neighboring conductors, and of periodic both in space and time; that is repelling them according to the laws of diamagnetism. The theory of the actions is known; though the nature of the whirls, as of the simple stream of electricity, is at present unknown.

[Here was shown a large electro-magnet and an induction-coil vacuum discharge spinning round and round when placed in its field.]

So much for what happens when electricity is made to travel along conductors, i. e., when it travels along like a stream of water in a pipe, or spins round and round like a whirlpool.

to say, the same appearances regularly recur at certain equal intervals of distance at the same time, and also present themselves at equal intervals of time at the same place; that in fact it belongs to the class of motions called by mathematicians undulatory or wave motions. The wave motion in this model (Powell's wave apparatus) results from the simple up-and-down motion popularly associated with the term wave. But when a mathematician calls a thing a wave he means that the disturbance is represented by a certain general type of formula, not that But there is another set of phenomena, it is an up-and-down motion, or that it usually regarded as distinct, and of looks at all like those things on the top another order, but which are not so dis- of the sea. The motion of the surface tinct as they appear, which manifest of the sea falls within that formula, and themselves when you join the pump to a hence is a special variety of wave mopiece of glass or any non-conductor, and tion, and the term wave has acquired in try to force the electricity through that. popular use this signification and nothing You succeed in driving some through, else. So that when one speaks ordinaribut the flow is no longer like that of ly of a wave or undulatory motion one water in an open pipe, it is as if the immediately thinks of something heavpipe were completely obstructed by a ing up and down, or even perhaps of number of elastic partitions or dia- something breaking on the shore. But

when we assert that the form of energy he was engaged in researches that no called light is undulatory, we by no other man can hope as yet adequately to means intend to assert that anything grasp and follow out: but, fortunately, whatever is moving up and down, or did not occur till he had published his that the motion, if we could see it, book on "Electricity and Magnetism," would be anything at all like what we one of those immortal productions which are accustomed to in the ocean. The exalt one's idea of the mind of man, kind of motion is unknown; we are not and which has been mentioned by comeven sure that there is anything like mo- petent critics in the same breath has the tion in the ordinary sense of the word "Principia" itself. at all.

But it is not perfect like the "Principia;" much of it is rough hewn, and requires to be thoroughly worked out. It contains numerous misprints and errata, and part of the second volume is so difficult as to be almost unintelligible. Some, in fact, consist of notes written for private use, and not intended for

Now, how much connection between electricity and light have we perceived in this glance into their natures? Not much, truly. It amounts to about this: That on the one hand electrical energy may exist in either of two forms-the static form, when insulators are electrically strained by having had electricity publication. It seems next to impossidriven partially through them (as in the Leyden jar), which strain is a form of energy because of the tendency to discharge and do work; and the kinetic form, where electricity is moving bodily along through conductors or whirling round and round inside them, which motion of electricity is a form of energy, because the conductors and whirls can attract or repel each other and thereby do work.

ble now to mature a work silently for twenty or thirty years, as was done by Newton two and a half centuries ago. But a second edition was preparing, and much might have been improved in form if life had been spared to the illustrious author.

The main proof of the electro magnetic theory of light is this. The rate at which light travels has been measAnd, on the other hand, that light is ured many times, and is pretty well the rapid alternation of energy from one known. The rate at which an electroof these forms to the other-the static magnetic wave disturbance would travel form where the medium is strained, to if such could be generated (and Mr. the kinetic form when it moves. It is Fitzgerald of Dublin thinks he has just conceivable, then, that the static form proved that it cannot be generated diof the energy of light is electro-static, rectly by any known electrical means) that is, that the medium is electrically strained, and that the kinetic form of the energy of light is electro-kinetic, that is, that the motion is not ordinary motion, but electrical motion-in fact that light is an electrical vibration, not a material one.

On November 5th, last year, there died at Cambridge a man in the full vigor of his faculties-such faculties as do not appear many times in a century -whose chief work has been the establishment of this very fact, the discovery of the link connecting light and electricity; and the proof-for I believe it amounts to a proof-that they are different manifestations of one and the same class of phenomena-that light is, in fact, an electro-magnetic disturbance. The premature death of James Clerk Maxwell is a loss to science, which appears at present, utterly irreparable, for

can be also determined by calculation from electrical measurements. The two velocities agree exactly. This is the great physical constant known as the ratio V, which so many physicists have been measuring, and are likely to be measuring for some time to come.

Many and brilliant as were Maxwell's discoveries, not only in electricity, but also in the theory of the nature of gases, and in molecular science generally, I can not help thinking that if one of them is more striking and more full of future significance than the rest, it is the one I have just mentioned-the theory that light is an electrical phenomenon.

The first glimpse of this splendid generalization was caught in 1845, five-andthirty years ago, by that prince of pure experimentalists, Michael Faraday. His reasons for suspecting some connection between electricity and light are not