by Thomas Brown, Surgeon, near Glasgow, &c.-Art. 45. Obfervations on the Solar Eclipfe which happened June 24, 1778; by William Wales, F. R. S. &c.-and Art. 46. An Account of the fame Eclipfe obferved at Leicester; by the Rev. Mr. Ludlam.

ART. VII. Philofophical Obfervations on the Senfes of Vision and Hearing; to which are added, a Treatise on Harmonic Sounds, and an Efay on Combuftion and Animal Heat. By J. Elliot, Apothecary. 8vo. 3 s. 6d. fewed. Murray. 1780.

TH

HIS collection of philofophical papers, and particularly thofe relating to Combuftion and Animal Heat, are the productions of a perfon evidently fmitten with the love of philofophy; and courting her, not unfuccefsfully; partly in the way of experiment, but principally (though, as it seems, not through choice) in the mode of theory and fpeculation.

In the first section, which relates to Vifion, the Author defcribes the appearances that occurred in an experiment made with a view to afcertain the fenfations that would be excited in the Retina, without the action of light upon it; by means of a violent and long-continued mechanical preffure made with the hands on the eye-balls, in the direction of their axes. A concave hemifphere of light first appears, chequered often in a very regular manner, with dark and lefs lucid intervals. Other appearances present themselves in fucceffion, on increasing the preffure till the eyes become quite hot; at which time the lucid appearance nearly equals that which is experienced at noonday, when the eyes are open. The reader will be in pain for the hardy Experimenter, as he proceeds in reading the Author's account of the fucceeding fenfations, till the time when the luminous appearances totally vanished; fo as not to be renewed on the continuance, or even increase, of the preffure. At this time the retina has loft all fenfation; fo that on removing the hands, and opening the eyes, the Author had the comfort to find himself totally blind; not being able to perceive the direct light of the fun itself. At length, however, but by degrees, the fenfibility of the organ is reftored.

This experiment,' fays the Author, is very painful,' (and, we will add, not a little hazardous) and it is not every one that would choose to repeat it after me, with the requifite care.' It is, we believe, a unique, and, we hope, will continue fo. For though, now that it has been made, we are much obliged to the Author for it; as fome of the appearances may throw new lights on certain difputed points relative to vifion; yet we would advife the curious reader to content himself with meditating only on the particulars that the Author has given of this fingular experiment,

As in this fection the Author defcribes luminous fenfations, which he had excited without the affiftance of light; fo in fome of the following fections he gives an account of what he calls internal founds, not excited by the vibrations of the external air, and which he had found means to produce, by preffing, dilating, or otherwise irritating the ear, at pleasure. These are not to be confounded with a mere ringing, or a rumbling and confused found in the ears: for the Author has, by practice and attention, and fometimes not without pain, as in the preceding cafe, been enabled to produce a regular though not complete fcale of diftinct founds; feveral of which he can excite with certainty, whenever he pleafes. It is very fingular too, that these founds do not vary, at different times, with refpect to acuteness or gravity; as he has found, by comparing them occafionally with the notes of a fixed mufical inftrument, with which they happened to be in unifon; though he can make them louder or weaker, by increafing or diminishing the irritation.

For example, he fays that he could not, for a long time, excite a found in his left ear, lower than what was in unifon with the middle D of a German flute: but he has fince produced one as low as B. In his right ear he can now go two whole tones lower, or down to G. In my left ear,' he adds, • I can raise notes from B to about an octave above, in all the intermediate gradations, or fenfible differences; but from thence, to a great part of another octave, I cannot yet excite them, though, ftit higher, they may be raised in great plenty, but in a more confufed manner.'

Were this fcale of internal founds complete, and the commodious but felfifh art of playing on a man's own ears-folus cum folo-eafily communicable, it would be pleafant enough to behold the gefticulations of the raw proficient in this art; who could not, like the fcraper on the violin, poffibly offend any one's ears but his own.-To be more ferious :-These trials of the Author give occafion to many obfervations and fpeculations on the organ and fenfe of hearing, that have at least novelty to recommend them to the inquifitive reader; to whose perufal we likewife refer a fubfequent fection on the harmonical founds, or fons flutes, as the French call them; which are made on the violin, violoncello, trumpet marine, and other inftruments played on with a bow, and which are produced by means of a flight preffure of the finger upon the ftring.

1. The principal part of this performance remains yet to be noticed; in which the Author propofes a new fyflem,-new at Jeaft at the time when this part of the work was compofed, and even when it was fent to the prefs-on the combustion of bodies, the cause of animal heat, and other fubjects connected with them. Under great difadvantages, and by dint of fpecu

lation,

lation, without having time or opportunities either for making experiments himself, or acquiring a knowledge of many that had been made by others; the Author had formed a theory to account for thefe phenomena, which remarkably agrees with that which Mr. Crawford has lately propofed to the world; but chiefly deduced from experiments actually made by the latter. Of this laft theory, and of the experiments on which it is eftablished, we lately gave a particular account, in our Review for November laft, page 378. Of the conformity of this laft hypothefis with that of our prefent theorift the reader will judge, from the following fhort account of it; fo far as it tends to explain the theory of combuftion.

When an inflammable body, alcohol for inftance, is fuffered to flame away; nothing but phlegm, an uninflammable substance, can be collected from it. The alcohol therefore has been intirely decompofed; and its phlogifton, in particular, has been feparated from it. Any quantity of air too, in which this procefs has been carried on till the flame has gone out, is found to be faturated with this principle, which the alcohol has loft, and which constituted it an inflammable fubftance.-Now, as the Aame, fays the Author, continued only while the air was taking the phlogifton from the vapour, and went out when the air was no longer able to do this; it feems that the combuftion depended intirely or fuch action of the air on the phlogiston.'

After obferving that the combination of certain fubftances with each other is attended with heat; Mr. Elliot fuppofes that the heat generated in the combuftion of bodies is occafioned. by the phlogiston, contained in the inflammable body, combining with the air; or, to ufe his own words, that air has a greater affinity with phlogifton, than the fubftances have with which it is combined in inflammable bodies; and therefore when all circumftances properly concur, it attracts that principle from thofe bodies; that a fhining heat is generated by their combination; and that this decompofition, when once fufficiently begun in a perfectly inflammable body, together with the fhining heat which is a confequence thereof, will be continued on the principles above laid down, without any farther affistance from extraneous heat, as long as any of the fubstance remains.'

Even in clofe veffels, where there is no communication with the external air, combuftion is neverthelefs maintained, and that too with violence, if nitre be mixed with the combustible body becaufe, fays the Author, it is now well known that nitre, or the nitrous acid, contains a quantity of common air, or rather indeed of air ftill more greedy of phlogiston, and therefore better adapted to promote combustion than common air. In the process of deflagration, the phlogiston, and this

air, diflodged from their respective bafes, fuddenly rush into union, and produce a fhining heat.

The Author illuftrates this doctrine in various manners, and not without occafionally referring to fome known experiments, from which he deduces confequences fubverfive of the prevailing theory relative to combustion; particularly of that part of it which fuppofes that phlogifton is combined elementary fire, let loofe, and rendered elaftic in that procefs; and that the heat and light of flame proceed from the avolation of this difengaged principle. He acknowledges that the light proceeds from it, though the heat does not; and that the latter proceeds from difengaged fire, as chemifts indeed at prefent imagine; who are miftaken only with refpect to the origin of that fire.

Hitherto the Author's hypothefis and that of Mr. Crawford nearly correfpond, though the two Writers had no communication with each other. In what follows, the present Author proceeds further, and varies from his brother theorift, when he inquires into the origin of the fire above mentioned. For this he accounts by an hypothefis, principally founded on a variety of conjectures more or lefs probable, and inferences from a few experiments; with respect to the attractive and repulfive powers, and other qualities, of the particles of air, fire, phlogiston, earth, and ather-not the chemical, but the hypothetical, fluid fo called.

The Author next, in a more experimental manner, confiders the phenomena of the light and colours exhibited by ignited fubftances; and then proceeds to apply fome of the preceding obfervations refpecting combuftion, to refpiration and animal heat (proceffes that bear a ftrong analogy to it), as well as to muscular motion. But here we must refer the Reader, who has a taste for fpeculations of this kind, to the work itself for information. The Author has given a favourable fpecimen of his ingenuity, at least, in fabricating a fyftem principally founded on fpeculation, that carries any face of confiftency in it, with fuch delicate and difficult materials to work upon as thofe above recited; the properties of fome of which are not well afcertained, and the very exiftence of one of them at leaft, is very problematical. Indeed it appears that the Author's fituation and circumstances have not furnished him with opportunities of following the more fafe and fober mode of ftrict experimental investigation. It would be unfair, therefore, and invidious in us, to mark any defects that we may have obferved in an attempt of this kind, made by a perfon thus circumftanced. For the fake, however, of the Author, as well as of those who perufe his performance, we take a pleasure in complying with a request, which he has tranfmitted to us by letter, to convey to

the

the public the following additional obfervations, where he rectifies his own errors, and this we shall do in his own words.

'Since the book was published,' fays Mr. Elliot, in his letter to us, I have, by a more attentive comparifon of it with Mr. Crawford's admirable difcoveries, convinced myself that I had erred in my idea of the manner in which fire exifts in bodies; though a prepoffeffion in favour of my own theory hindered me from perceiving it before.-I had imagined that it exifted in bodies only in its elaftic ftate, as defcribed in the first five cafes of the feventh fection. When air is heated and cooled, the phænomena feem to answer to that theory; and do not the expanfion of bodies, and the feparation of their particles by heat, depend on the fame principle? Fixable air, however, is not much jefs elaftic than common or dephlogisticated air; though the former, by Mr. Crawford's experiments, contains 67, and the latter near 300 times more fire. Their specific gravities are to one another only as the numbers 281, 187, 185, or thereabout; and, confequently, the fire which is extricated by phlogiston was in a fixed or combined ftate. And, with regard to their elafticities, I have this to obferve; that, as bodies which contain moft phlogifton refract light moft ftrongly; fo bodies which contain the greatest quantity of fire in a fixed state attract elastic fire moft powerfully in the manner described in the cases above alluded to. But, as happens with the refraction of light, this difference will be but fmall, though the different proportions of fire in the bodies be very great, and only perhaps fuch as to answer to the numbers given above. The elafticity of air, the expanfion of bodies by heat, and the feparation of their particles, depend therefore on these principles;-the fenfible heat, on the attraction of bodies for fire, or abfolute heat, according to the law in Cafe 11th, &c. and their abfolute quantities of fire, on the quantity of phlogifton, and the force of its combination; or, in other words, on the attraction of those bodies for fire. It appears, therefore, that I was right enough in my facts in these cafes; but, through not distinguishing the two kinds of attraction, wrong in my manner of explaining them.'

On the whole, we cannot help being greatly prejudiced in favour of our prefent theorift; on account of the many marks of real ingenuity exhibited in this performance; particularly in the theory relating to combuftion and refpiration. His merit in this refpect is the greater, as it evidently appears, from various paffages that occur in this work, that his neceffary avocations, and other circumstances, had not enabled him to know what had been done by others, or to make the neceffary experiments himself. He is entitled to equal praife on account of his unafluming manner, and the great candour, and even warmth, with