that they are of little weight in determining the question, respecting the nature of heat, which has so long divided chemical philosophers. We ought to observe, that these experiments were made to prove the corporeal nature of caloric; for if heat can be weighed, the question respecting its materiality is at once decided. They consisted in dissolving salt in water, and weighing the solution after the absorption of caloric had ceas ed; 2dly, in adding sulphuric acid to water,and ascertaining the weight of the compound when it had fallen to the temperature of the ingredients before they were mixed. The conclusions, drawn from these experiments, are very remarkable. He affirms, that they gained or lost half a grain in weight for every ounce of the mixture, and his inference, presuming on their accuracy, is very natural, that heat is matter.' Now experiments to determine this question were made so long ago as the age of De Luc of Geneva, and they have been repeated and varied by Lavoisier, Dr. Fordyce, and Count Rumford, with the most scrupulous exactness, without any general acquiescence in the belief of either doctrine. Those of the latter were characterised by delicacy of instruments and accuracy of calculation. Yet notwithstanding this combination of circumstances, which promised some positive conclusion, he was unable to detect either the accession, or loss of weight, in the heating or cooling of bodies. Consequently, the inference which he drew was, 'that neither the addition nor abstraction of caloric, makes any sensible alteration in the weights of bodies."* The weight which Dr. Ewell gives to caloric, in his

Thompson's Chemistry, 2d ed. vol. 1. p. 308. Nicholson's Journal, 4to. series, vol. 3. p. 381.

experiments, is not far from that of a cubick inch of atmospherick air; yet, is it possible to believe, that this substance, which from its excessive tenuity has been termed unconfinable, can equal in specifick gravity another, which is confinable, almost tangible, and as easily managed as many liquid bodies? If the proof of the materiality of caloric depended solely on these experiments, the advocates of the contrary theory, we think, would have little trouble in establishing their positions.

In common with most systematick writers on chemistry, Dr. Ewell commences his discourse on light with a detail of its physical properties. In speaking however of the refraction, which the solar rays suffer in their passage from a rare to a dense medium, he has committed an important errour, which has probably escaped detection merely from the inattention of the author. In proof of the refractive power of the atmosphere he affirms, that

the sun sets and rises earlier, than appears to spectators.' Now, almost the converse of the proposition is true. In consequence of the refraction, which the rays of light suffer in their passage from a rarer medium through our atmosphere, the sun is apparently above, before he has actually reached, the plane of the horizon. Dr. Ewell surely cannot be ignorant of this fact, nor that the degrees of refraction at different altitudes have been accurately calculated by several eminent astronomers, particularly by Sir I. Newton, Mr. Simpson, and Dr. Bradley, whose tables may be seen in any elementary work on astronomy. Consequently, the sun rises later and sets earlier, than appears to the inhabitants of the earth. We are now to view our

* Enfield's Institutes, p. 256-7. Ferguson's Astronomy, 4th ed. p. 92.

author as the opponent of the illustrious Newton. We are always tempted to suspect, that when a young man commences an attack on universally received doctrines, which, in fact, are considered by the world as axioms in philosophy, he is actuated more by vanity,than the genuine spirit of philosophical inquiry. Dr. Ewell has underta ken to overthrow the theory of the prismatick colours, and to erect on its ruins his own more ingenious hypothesis. But we recommend to him the observation of the ancient poet,

'Non omnia possumus omnes.' He may be a good chemist, but he is no optician. It may not be amiss, however, to notice the arguments, which he adduces to disprove the correctness of these principles. He thinks, that the experiment of decomposing a ray of light by the refractive power of the prism, and the subsequent union of the primitive colours so as to produce the original ray, by no means conclusive. He goes on to observe, that if the doctrine of the composition of light were true, it could not account for all the colours of bodies. To suppose, that blackness is the consequence of the absorption of all the light must be absurd; since it is only by the reflection of light that we are enabled to see black bodies; and since those, which are transparent, and of course allow the light to pass through them, are very far from being black. That whiteness does not proceed from the reflection of all the light is shown by the circumstance, that the whiteness of bodies is not in proportion to their reflection of light. Hence mercury, polished iron, and other metals, reflect more light, than the whitest paper.' The futility of these objections will appear obvious to all, who are acquainted with the doctrine of light,

2.

and the laws, by which it is governed in its passage through diaphanous, and its reflection from opake bodies. It is true, that black bodies are seen by reflection, but this light is reflected from coloured bodies in their neighbourhood. When a black object is placed so as to intercept a portion of light, those rays, which pass along its edges, define its figure and mark its boundaries; and it is thus more by the interception of the rays of light from other bodies, that black substances are seen, than by its reflection from their own surfaces. The reason why diaphanous bodies do not appear black is, that they are capable of transmitting the rays of light, which Dr. Ewell thinks should produce that colour. While the sun is above the horizon, an immense body of light is continually flowing from different objects. These secondary, or reflected rays, passing in all directions, must necessarily, in some cases, strike up-' on these diaphanous bodies and be either reflected or transmitted, in consequence of which the latter will appear more, or less coloured. It is a well known fact, that objects are always seen more or less distinctly thro' such substances,arising from the less or greater refraction of these accidental rays of light. 3. It is not necessary to the truth of the Newtonian doctrine of colours, that bodies must reflect all the light which fall on their surfaces. It is only necessary, that that portion, which is reflected, should be undecompounded, or be still composed of the seven prismatick colours. Consequently a body may appear white, which still transmits a portion of light, impelled on its surface. The truth of this observation has been demonstrated. According to the photometric experiments of Mr. Leslie, of 100 parts of incident light vellum pa

per transmitted 49 parts, and thin post 62. Our author next proceeds to the consideration of the theory lately advanced by some English philosophers, respecting the calorific and de-oxidizing solar rays. Of this he is an unbe liever, and of course is very brief. He has mentioned neither the names, nor the experiments of Herschell, Wollaston, Ritter, and Englefield; and he dismisses the subject almost without comment, with this single observation, that it is too complex to be true'!

We shall now present our readers with Dr.Ewell's own theory of colours. He observes, that, our ideas of the colour of bodies appear to depend solely on the peculiar modification or motion of light given by the reflective surfaces. These reflective surfaces probably receive their respective powers, in consequence of peculiarities in their mechanism or organization.' Upon the supposition, that light is a homogeneous body, which it seems is the idea of our author, we can conceive of no other physical alteration it may undergo, by its appulsion on a hard body, than some change in the figure of its particles. But we have no proof, that this change of form does take place, nor ⚫ that the surfaces of bodies are capable of producing this effect. We cannot conceive that colour should depend on any peculiar mechanism of matter. All the particles, how ever smail, of a substance, when aggregated must form a mass, whose reflective surfaces are at least equal in number to the molecules of that body. Now each of these, we presume, is a plane surface with regard to the incidence of the rays of light; consequently, in what

ever mode these surfaces are ar ranged, they can only reflect the light in an angle equal to that of incidence, which, thus reflected, may strike on other surfaces, and be reflected ad infinitum without any change of properties, and at length will reach the eye, where they will excite sensations differing, not in nature, but only in intensity. It will be evident to all, that a difference of motion of the rays of light can only excite corresponding stronger or weaker impressions on the retina, and consequently that these can be followed by percep tions only of different degrees or quantities of light. In support of his opinion, our author brings as proofs, that coloured liquids vary in colour as their position, with regard to the eye, is altered; and, 2, the appearance which the clouds present before the rising, and after the setting, of the sun. It is unnecessary, we presume, to take up more of the time of our readers in answering these objections. We have already exceeded the limits of a common review, and have reason to fear that it has become as tedious as a "tale twice told." We shall, therefore, finish the subject of light, by noticing another hypothesis of Dr. Ewell, on the agency of this substance in the production of the yellow fever. We mean not to enter on the discussion of its merits. It will be sufficient to observe, that from the nature of light, it appears inadequate to the effects ascribed to it in this theory, and that the phenomena can be more rationally explained on the principle of the action of caloric on putrescent animal and vegetable substances. It remains for us, therefore, only to advert to the two other unconfinable substances, electricity and galvanism. We could not help admiring the lucid manner in which

our author defines the latter. GalVanism,' says he, resembling, in a few of its properties, the electrick fluid, is one lately and accidentally discovered by an Italian, and which is generally termed galvanism, or animal electricity.' In fewer words, galvanism is a fluid, generally termed galvanism!

Under the head of electricity Dr. Ewell attempts to account for the production of light, during the passage of the electrick fluid from one conductor to another, or from the clouds to the earth, by supposing that the latter diminishes or destroys the capacity of the air for the former. He quotes no authority in support of his opinion, nor does he mention the names of any of those philosophers, from whom he probably first received it. Indeed, from the manner in which it is introduced, his readers might be 'disposed to believe, that he was the person, in whom it first originated. Now Mr. Berthollet was the first, who attempted to account for the evolution of light and caloric from substances, acted upon by the 'electrick fluid, by supposing, that their capacities for these elements were very much diminished in consequence of the sudden and violent compression of their particles.* This idea was more fully developed in a paper, read to the National Institute of France, by M. Biot, which has since been translated and re-published in Nicholson's Philosophical Journal. It was afterwards noticed by the editor of this periodical publication, and seems to have attracted the attention of Mr. Leslie, who had even written an essay on the subject, though it was never published.§

Berthollet's Chemical Staticks.
Vol. 12. p. 212.
Vol. 13. p. 89-90.
Leslie on Heat. Note 17.

1

This theory is plausible and ingenious; but there is one strong objection, which is, that the luminous spark often appears stationary on the point of the conductor, and in that situation it is apparently as brilliant, as when moving with great velocity through the air. In this state, it is difficult to conceive, that the air should be so forcibly compressed, as to lose its capacity, and consequently evolve the light and caloric, with which it was combined.

We have thus finished the review of those simple elementary substances, which are termed by Dr. Ewell, on the authority of Thompson and Fourcroy, unconfinable. We have been more diffuse in our examination from a belief, that they contained much false theory and incorrect statement, and this is the only apology we have to offer for our prolixity. In our next number we shall finish our observations on this work by considering its more immediate object, the application of the principles of chemistry to domestick affairs or to those arts, on which the ease and comfort of society essentially depend.

[To be continued.]

ART. 11.

The Wanderer of Switzerland, and other Poems, By James Montgomery. Boston Greenough, Stebbins, & Hunt, and J. F. Fletcher. 1807. 18mo. pp. 177.

WE claim some regard for hav ing first brought this beautiful collection from the solitary corner of a shop into general notice, by publishing some of the shorter odes in our poetical department. The Muses of England do not often utter sweeter notes, than these, combining the simplicity of Burns