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respecting the latter, which not only are well known to be founded, but are also best calculated to elucidate the comparison. These are the seven following:-1. Light, both solar and terrestrial, is a sensation occasioned by rays emanating from luminous bodies; 2. These rays are subject to the laws of reflection; 3. They are refrangible; 4. They are of different refrangibility; 5. They are liable to be detained by different diaphanous bodies; 6. They are liable to be scattered on rough surfaces; and 7. They have hitherto been supposed to have a power of heating bodies, which however remains as yet to be examined.

The similar propositions respecting heat which the Doctor intends to prove, are as follows:-1. Heat, both solar and terrestrial, is a sensation occasioned by rays emanating from candent substances; 2. These rays are subject to the laws of reflection; 3. They are refrangible; 4. of different refrangibility; 5. liable to be detained in their passage through other bodies; 6. liable also to be scattered on rough surfaces; and lastly, They may be supposed, when in a certain state of energy, to have a power of illuminating objects; which last, however, remains as yet to be examined.

The paper before us is limited to the experiments on the three first of the above-mentioned comparative propositions. They are twenty in number, of which the ten first relate to the reflection, and the ten last to the refraction of these rays, under all the variety of circumstances deducible from the different kinds of heat above enumerated; to which are added, some attempts to produce a condensation of heat independent of light, by spherical mirrors and lenses. Such mirrors and lenses, together with accurate thermometers, were the instruments used in these experiments, of which those on invisible solar heat, and invisible culinary rays, are perhaps the most striking, as they serve to corroborate the theory laid down by the Doctor in a former paper concerning the existence of such heat and rays independent of light.

It being impracticable to epitomize the ample account of these experiments given in the paper, we must content ourselves with observing in general, that all their results fully evince the truth of the second and third propositions above laid down, viz. that the rays which occasion heat, both solar and terrestrial, in all their different kinds, and under every variety of circumstances that could be devised, are subject to the laws of reflection and refraction.

The same results also convey sufficient evidence of the radiant nature of light; and hence equally prove the first of those propositions. The three following ones, viz. the fourth, fifth, and sixth, are reserved for a future communication; where the author proposes likewise to enter into a discussion concerning the seventh or last of them, relating to the power of heating and illuminating.

Chemical Experiments on Zoophytes; with some Observations on the component Parts of Membrane. By Charles Hatchett, Esq. F.R.S. Read June 12, 1800. [Phil. Trans. 1800, p. 327.]

Having completed the series of experiments on the component parts of shell and bone which he described in a former paper, it was suggested to Mr. Hatchett that there still remained a large class of substances belonging to the animal kingdom, namely, the various species of Zoophytes, which had never yet been carefully analysed, and the investigation of which would probably lead to some curious, and perhaps useful inferences. Although aware of the extensiveness of the inquiry, he yet readily engaged in it; and we have now before us the fruit of his indefatigable industry and ardent zeal for the advancement of science.

The first part of the paper contains a full account of the series of experiments he made on the abovementioned substances, which, in the present pressure for time, we must pass over unnoticed in order to hasten to the second, which consists of observations on those experiments, in the course of which the subject necessarily led to an inquiry into the nature and properties of several other analogous substances, such as horn, nail, hoof, quill, hair, feathers, tortoiseshell, the scales of fish, amphibious animals and insects, albumen, and even muscular fibre.

We must here recollect that in his former paper on shell and bone Mr. Hatchett had arrived at the conclusion that their essential ingredients were carbonate of lime in the former, and phosphate of lime in the latter, the bases in both consisting of different modifications of a glutinous, gelatinous, or membranaceous substance. This conclusion he had the satisfaction of seeing corroborated, and the chain of connexion widely extended, by the facts deduced from the present inquiry. The general results of which are, that the Madrepores and Millepores (like several of the shells) are formed of a gelatinous or membranaceous substance, hardened by carbonate of lime, the difference consisting only in the mode in which these materials are combined: that in the Tubipora, Flustra and Corallina, some phosphate of lime is mixed with the carbonate of lime: that in the Isis the basis is a regularly organized membranaceous, cartilaginous and horny substance, hardened by carbonate of lime, one species only (the Isis ochracea) yielding also a small proportion of phosphate of lime. That the hardening substance of the Gorgonia nobilis is likewise the carbonate of lime, with a small portion of phosphate; but that the matter forming the membranaceous basis consists of two parts, the interior being gelatinous, and the external a complete membrane, so formed as to cover the stem in the manner of a sheath or tube. That the other Gorgoniæ consist of a horny stem coated by a membrane, which is hardened by carbonate of lime. That the Sponges are of a nature similar to the horny stems of the Gorgoniæ, and only differ from these and from each other by the quality of texAnd lastly, that the Alevonia are likewise composed of a soft

ture.

flexible membranaceous substance, very similar to the cortical part of some of the Gorgoniæ; and in like manner slightly hardened by carbonate, mixed with a small portion of phosphate of lime.

From this mass of evidence we collect, in general, that the varieties of bone, shell, coral, and the numerous tribe of Zoophytes with which the last are connected, only differ in composition by the nature and quantity of the hardening or ossifying principle, and by the state of the substance with which this principle is mixed or connected; the gluten, or jelly, which cements the particles of carbonate or phosphate of lime, and the membrane, cartilage, or horny substance which serves as a basis, appearing to be only modifications of the same substance, which progressively graduates from a viscid liquid, or gluten, into a gelatinous substance, which again, by increased inspissation, and by the more or less perfect degrees of organic arrangement, forms the varieties of membrane, cartilage, and horn, which it seems form the peculiar differences of the several species.

It is obvious that in this inquiry much depends upon an accurate investigation of the gluten, or jelly, so often mentioned as a principal ingredient in the substances under examination. This gave rise to the experiments on the analogous substances above mentioned, which led to a better acquaintance with the substance which now obtains the name of gelatin.

Not being allowed to enter into a detail of these experiments, we shall only observe at present, that this gelatin is a component part of most of the animal substances above enumerated; that it varies in quality from a very attenuated jelly or mucilage, to that viscid substance called glue, the varieties of which also differ in solubility and tenacity that it is present in various proportions, so that certain bodies, such as the cutis and cartilages of the articulations, seem to be entirely formed by it; while others, like nail, quill and tortoiseshell, can hardly be said to contain any; and that by its presence in various states and proportions, it may be regarded as the principal cause of those degrees of flexibility, of elasticity and of putrescibility, so various in different parts of animals.

In all these substances, when all the gelatin they contained had been separated, either by repeated boiling in water, or by being steeped in dilute acids, a more insoluble substance remained of a very different nature from the gelatin, and which became the object of another extensive analysis. The results here led to the curious and important conclusion, that the substance known by the name of albumen is in fact the primary animal matter from which all the others, and even the gelatin and the animal fibre, are ultimately derived, the formation of the two latter beginning with the process of sanguification in the fœtus, and the immense variety in the animal creation being deducible from the infinite diversity and modifications in texture, flexibility, elasticity, and other properties of the same substance composing the several parts which constitute the bodies of animals.

On the Electricity excited by the mere Contact of conducting Substances of different Kinds. In a Letter from Mr. Alexander Volta, F.R.S. Professor of Natural Philosophy in the University of Pavia, to the Rt. Hon. Sir Joseph Banks, Bart. K.B. P.R.S. Read June 26, 1800. [Phil. Trans. 1800, p. 403.]

In prosecuting his experiments on the electricity produced by the mere contact of different metals, or of other conducting bodies, the learned Professor was gradually led to the construction of an apparatus, which in its effects seems to bear a great resemblance to the Leyden phial, or rather to an electric battery weakly charged; but has moreover the singular property of acting without intermission, or rather of re-charging itself continually and spontaneously without any sensible diminution or perceptible intervals in its operations. The object of the present paper is to describe this apparatus, with the variety of constructions it admits of, and to relate the principal effects it is capable of producing on our senses.

It consists of a long series of an alternate succession of three conducting substances, either copper, tin and water; or, what is much preferable, silver, zinc, and a solution of any neutral or alkaline salt. The mode of combining these substances consists in placing horizontally, first, a plate or disk of silver (half-a-crown, for instance,) next a plate of zinc of the same dimensions; and, lastly, a similar piece of a spongy matter, such as pasteboard or leather, fully impregnated with the saline solution. This set of three-fold layers is to be repeated thirty or forty times, forming thus what the author calls his columnar machine. It is to be observed, that the metals must always be in the same order, that is, if the silver is the lowermost in the first pair of metallic plates, it is to be so in all the successive ones, but that the effects will be the same if this order be inverted in all the pairs. As the fluid, either water or the saline solution, and not the spongy layer impregnated with it, is the substance that contributes to the effect, it follows that as soon as these layers are dry, no effect will be produced.

This apparatus, when it consists of only twenty pairs of metallic plates, is already capable not only of giving to Cavallo's electrometer, with the aid of a condenser, signs of electricity as high as 10° or 15o, and of charging the condenser by a simple touch to such a degree as to give a spark; but it will also give to two fingers of the same hand, the one touching the foot and the other the top of the column, a succession of small shocks, resembling those occasioned by a Leyden phial, or a battery weakly charged, or by a torpedo in a weak condition. These effects will be increased if the communication be made through water; for which purpose the bottom of the column may be made to communicate, by a thick metallic wire, with water contained in a basin or large cup. A person who now puts one hand into this water, and with a piece of metal held in the other hand touches the summit of the column, will experience shocks and a pricking pain as high as the wrist of the hand plunged in the water, and even some

times as high as the elbow, while in some cases even the wrist of the other hand will experience a similar sensation.

It has been ascertained by repeated trials, that these effects are stronger in proportion to the greater distance of the metallic pairs, which are made to communicate. Some sensation will be produced when the foot of the column is connected with the third or fourth pair, but it will perceptibly increase as we proceed further towards the summit. This naturally led to an extension of the column much beyond the number of metallic pairs above mentioned; and expedients are here suggested for rendering such extended columns stable and at the same time sufficiently manageable. With a column of about sixty pairs of plates, shocks have been felt as high as the shoulder; such a column may be even divided into two or three distinct cylinders, which being well connected by metallic conductors, will be equally powerful and much more convenient.

Among various other modes of applying the same agents, the author describes an apparatus in which the fluid is interposed between the metals without being absorbed in a spongy substance. This consists of a number of cups or goblets, of any substance except metals, placed in a row either straight or circular, about half filled with a saline solution, and communicating with each other so as to form a kind of chain, by means of a sufficient number of metallic arcs or bows, one arm of which is of silver, or copper plated with silver, and the other of zinc. The ends of these bows are plunged into the liquid in the same successive order, namely, the silver ends being all on one side, and those of zinc on the other,-a condition absolutely necessary to the success of the experiments, it having been observed that if out of sixty bows, for instance, the twenty intermediate ones be turned in the opposite direction from the remainder, the effects produced by the apparatus will be far less perceptible.

It was observed, that if a circular communication be completed by means of a bow connecting the first and last of a long series of cups, two hands, or even two fingers plunged into one of these cups will still receive an electric sensation. This is explained by admitting the fact, that warm animal substances, and particularly their fluids, are in general better conductors than water.

The sensible effects of either of these apparatus, composed of forty or fifty links, do not, it seems, consist merely in shocks, contractions, or spasms in the muscles or limbs; but, besides affecting the sense of touch, they are also capable of exciting an imitation in the organs of taste, sight, and even hearing. A particular account is given of these singular effects, from which we learn, that the more sensible the parts are which are exposed to the impressions of this agent, the more quick will be the sensation;-that as to taste, we have only to recollect the experiments formerly described by the author, in which the tongue was sensibly affected by the combination of two metals applied to each side of it;-that with respect to the sense of vision, the sparks yielded by this apparatus are sufficient evidence of the effect, certain expedients only being necessary for facilitating the

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