versally considered as the coolest that can be worn in very hot weather, and especially when a person is exposed to the direct rays of the sun; and if they are well calculated to reflect calorific rays in summer, they must be equally well calculated to reflect those frigorific rays by which we are cooled and annoyed in winter.

Garments of fur are warmer in cold weather when worn with the hair outwards, than when it is turned inwards. Is not this a proof that we are kept warm by our clothing, not so much by confining our heat as by keeping off those frigorific rays which tend to cool us? The fine fur of beasts, being a highly polished substance, is calculated to reflect those rays which fall on it; and if the body be kept warm by the rays which proceed from it being reflected back upon it, a fur garment would be warmest when worn with the hair inwards; but if it be by reflecting and turning away the frigorific rays from external and colder bodies, that we are kept warm by our clothes, we might expect that a pelisse would be warmest when worn with the hair outwards, as the Count says, in fact, it is.

The fur of several delicate animals becomes white in winter in cold countries; and that of bears, which inhabit the polar regions, is white in all seasons. These last are exposed alternately in the open air to the most intense cold, and to the continual action of the sun's rays during several months. If it should be true that heat and cold are excited in the manner above described, and that white is the colour most favourable to the reflection of calorific and frigorific rays, it must be acknowledged that these animals have been exceedingly fortunate in obtaining clothing so well adapted to their local circumstances.

Observations on the Change of some of the proximate Principles of Vegetables into Bitumen. By Mr. HATCHETT. BODIES, formerly appertaining to the organised kingdoms of nature, after the loss of the vital principle, become gradually converted into fossil substances. In some cases, this conversion is so complete, as to destroy all traces of previous organic arrangement; but in others the original texture and form have been more or less preserved, though the substances themselves are decidedly mineral. Some of these extraneous fossils retain part of their original principles, whilst others can only be regarded as casts or impressions. Mr. Hatchett selects from the animal kingdom, as examples, among others,

the fossil ivory, which retains its cartilage; the bones in the Gibraltar rock, consisting of little more than the earthy part or phosphate of lime. The vegetable kingdom has likewise produced many striking instances; and animal petrifactions are commonly of a calcareous nature, but vegetable petrifactions are generally siliceous.

Mr. Hatchett's main object is to adduce some proofs, that the bituminous substances are derived from the organised kingdoms of nature, and especially from vegetable bodies. The chemical characters of the pure or unmixed bitumens, such as naphtha, mineral tar; &c. are, in certain respects, so different from those resins and other inspissated juices of recent vegetables, that, had the former never occurred but in a separate and unmixed state, no positive inference could have been drawn from their properties, in proof of their vegetable origin. Fossil animal substances form a series, commencing with such as are scarcely different from those which are recent, and terminating in productions which have totally lost all traces of organisation.

Similar instances are afforded by the vegetable kingdom: the three examples cited in this paper are, 1. The submarine forest at Sutton, on the coast of Lincolnshire, the timber of which has not suffered any very apparent change in its vegetable characters. 2. The strata of bituminous wood, called Bovey coal, found at Bovey, in Devon, which exhibits a series of gradations, from the most perfect ligneous texture, to the substance nearly approaching the characters of pit-coal, and, on that account, distinguished by the name of stone-coal. 3. The varieties of pit-coal, so abundant in many parts of this country, in which almost every appearance of vegetable has been destroyed.

These examples appear to form the extremities and centre of the series; but as the process of carbonisation, and formation of bitumen, has not taken place in the first instance, and as these effects have proceeded to the ultimate degree in the last, it seems most proper to seek for information, and for positive evidence, in the second example, which appears to be the mean point, exhibiting effects of natural operations, by which bitumen and coal have been imperfectly and partially formed, without the absolute obliteration of the original vegetable characters.

After a minute and accurate description and analysis of the bitumen from Bovey coal, it is inferred by Mr. Hatchett, that it is a peculiar and hitherto unknown substance, which is partly in the state of vegetable resin, and partly in that of

the bitumen called asphaltum, the resin being in the largest proportion, as 100 grains of it afforded:

Resin
Asphaltum
Earthy residuum

55

41

3

99

Thus we have an instance of a substance being found under circumstances which constitute a fossil, although the characters of it appertain partly to the vegetable and partly to the mineral kingdom.

Time alone does not reduce animal or vegetable bodies to the state of fossils. There are examples of whole forests which have been submerged prior to any tradition, and which, nevertheless, completely retain their ligneous characters. Other causes and agents must therefore have been required to form the varieties of coal, and other bituminous substances. In some instances, as in the formation of Bovey coal, these causes seem to have acted partially and imperfectly, while, in the formation of the greater part of the pitcoals, their operation has been extensive and complete.

In the pit-coals, the mineral characters predominate, and the principal vestige of their real origin seems to be bitumen, for the presence of carbon in the state of oxide cannot alone be considered as decisive. Bitumen, therefore, with the exuvia and impressions so commonly found in the accompanying strata, must be regarded as proofs in favour of the origin of pit-coal from organised bodies; and, considering the general facts, which have been long observed, together with those lately adduced respecting the Bovey coal, and the substance, found with it, we seem to have evidence, that bitumen has been produced by the modification of some of the proximate principles of vegetables, and especially resin.

On Muscular Motions. By ANTHONY CARLISLE, Esq.

MUSCULAR motion is the first sensible operation of animal life the various combinations of it sustain and carry on the multiplied functions of the largest animals: the temporary cessation of this motive faculty is the suspension of the living powers; its total quiescence is death.

The muscular parts of animals are most frequently composed of many substances in addition to those which are purely muscular. In this gross state, they constitute a flex

ible, compressible solid, whose texture is generally fibrous, the fibres being compacted into fasciculi, or bundles of various thickness. These fibres are elastic during the contracted state of the muscles after death, being capable of extension to more than one-fifth of their length, and of returning again to their former state of contraction. This elasticity, however, appears to belong to the cellular membrane, and not to the matter of the muscle.

The attraction of cohesion, in the parts of the muscle, is strongest in the fibres, being double that of the transverse direction. When muscles are capable of reiterated contractions and relaxations, they are said to be alive, or to possess irritability. This quality fits the organ for its functions. When muscles have ceased to be irritable, their cohesive attraction in the direction of their fibres is diminished, but it remains unaltered in the transverse direction.

In speaking of temperature as having an essential influence over the actions of the muscles, and of respiration as one of the known causes which influences the temperatures of animals, the following facts deserve notice :

Diminished respiration is the first step into the state of torpidity: a deep sleep accompanies it; respiration then ceases altogether; the animal temperature is totally destroyed, coldness and insensibility take place, and finally, the heart concludes its motions, and the muscles cease to be irritable. It is worthy of remark, that a confined air, and a confined respiration, ever precede these phenomena: the animal retires from the open atmosphere, his mouth and nostrils are brought into contact with his chest, and enveloped in fur; the limbs become rigid, and the blood never coagulates during the dormant state. On being roused, the animal yawns, the respirations are fluttering, the heart acts slowly and irregularly, he begins to stretch out his limbs, and proceeds in quest of food. During this dormancy, the animal may be frozen, without the destruction of the muscular irritability, and this always happens to the garden snail, and to the chrysalides of many insects during the winter of this climate.

The loss of motion and sensation, from the influence of lower temperature, accompany each other, and the capillaries of the vascular system appear to be contracted by the loss of animal heat, as in the examples of numbness from cold. Whether the cessation of muscular action be owing to the impeded influence of the nerves, or to the lowered temperature of the muscles themselves, is doubtful; but the known influence of cold upon the sensorial system, rather favours

the supposition, that a certain temperature is necessary for the transmission of nervous influence, as well as sensation.

From other experiments, it appears that the irritability of the heart is inseparably connected with respiration; and that, according to the nature of the inhaled gas, the actions of the heart are altered or suspended, and the whole muscular and sensorial systems partake of the disorder.. The blood appears to be the medium of conveying heat to the different parts of the body, and the changes of animal temperature are connected with the degree of rapidity of the circulation.

In considering the causes which occasion the loss of muscular irritability, we are referred to workmen whose hands are exposed to the contact of white lead, the torpidity of whose muscles seems to be decidedly local, because, in many instances, neither the brain nor the other members partake of the disorder, and it generally affects the right hand. A chemist has frequently experienced spasms and rigidity in the muscles of his fore arms, from the effusions of nitric acid over the cuticle of the hand and arm. The use of mercury occasionally brings on a similar rigidity in the masseter muscles.

A smaller quantity of blood flows through a muscle during the state of contraction than during the quiescent state, as is evinced by the pale colour of the red muscles when contracted. But when the muscles are vigorously contracted, their sensibility to pain is nearly destroyed: this mean is employed by jugglers, for the purpose of suffering pins to be thrust into the calf of the leg and other muscular parts with impunity.

The human muscles are susceptible of changes from extraordinary occurrences of sensible impressions. Long attention to interesting visible objects, or to audible sensations, exhausts muscular strength: intense thought and anxiety weaken the muscular powers, and the passions of grief and fear produce the same effect suddenly, while the contrary feelings give more than ordinary vigour. To conclude: there are two states of the muscles; one active, or that of contrac-' tion; the other a state of ordinary tone, which may be considered as passive, as far as relates to the mind; but the nervous power seems never to be quiescent, as it respects either the voluntary or involuntary muscles during life. The yielding of the sphincters appears to depend on their being overpowered by antagonist muscles rather than on voluntary. relaxation.