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 i£ T H ( 32 the way Q^esperiment, which had led him to his former difcoveries, but in the way of conjefture, which will never lead any man to truth. He had recourfe to a fubtile elaftic scther, not much different from that of the ancients, and by it accounted for every thing he did not know, fuch as the caufe of gravitation, mufcular motion, fenfation, lire. Notwithftanding the reputation of Sir Ifaac, philofophers have generally looked upon this attempt as the foible of a great man, or, at lead, as the mod ufelefs part of his v/orks ; and accordingly perufe it rather as a dream or a romance, than as having any connexion with fcience. But v/e are forry to find, that fome late attempts have been made to revive this doftrine of sether, particularly in a differtation De ortu animaliu.ni caloris, publilhed in May lad. As the revival of an old do&rine becomes in fome meafure a new one, we (hall plead no other apology for inferting a fpecimen of the method of reafoning employed in this differtation. The author makes frequent ufe of a fpecies of argument termed dilemma by logicians. For example, in the fird part of the work, after endeavouring to prove that animal heat cannot be owing to fermentation, the motion of the fluids, and other caufes that have 64 ufually been affigned, he draws this conclufion:— If none of thefe caufes are fuffeient to produce jthe 44“ effeft; therefore^ by dilemma,” fays he, “ it ,mud be fought for in the nature and aCtion of the nerves.” —This is a new fpecies of dilemma: —If the author had proved, that the caufe of heat in animals could not poflibly exid any 'inhere, but either in fermentation, the motion of the fluids, <bc. or in the nerves, after having difprpved its evidence in all the red, his conclufion in favour of the nerves would have been jud; but, as he has not fo much as attempted this, the conclufion is not only falfe, but ridiculous. However, upon the authority of this dilemma., the author fird gives what he calls a Corapend of a new doctrine concerning the nerves, and then proceeds to inquire in what44manner the nerves produce animal heat: He tells 44 us, That thought [c-ogitatio) and fenfation depend 44 uponimpulfes either on the extremities of the nerves, 44 or the fenforium commune, and the confequent motions produced by thefe impulfes: That thefe motions 44 are fo quick, as to be almod indantaneous: That as 44 all motion is mechanical; therefore thought, fen44 fation, and mufcular motion, mud likewife be me44 chanical: That fuch quick motions cannot be p.ro44 duced without the intervention of fome extreme44 ly eladic power; and, as Sir Ifaac Newton has 44 fhown, that the impulfes which occafion the diffe44 rent fenfations mud be owing to an elaflic power; 44 therefore the mufcular motions of animals mud be 44 occafioned by the44ofcillations offome eladic power.” 44 But,” fays he, as this eladic power cannot exid in the folid nervous fibres, nor in any ineladic “44 fluid; therefore, by dilemma, it mud exid in an 44 eladic fluid; and hence alfo, by the former dilemma, C4 this eladic fluid mud be feated, either in the nerves, or in their medullary fubdance,”

) M T H Here 44again the'author calls Sir Ifaac into his aflidance.— What confirms this opinion,” fays he, 44 is 44 44 the Newtonian aether, which pervades all nature, 44 and which, with a few variations in its modification, Sir Ifaac has Ihown to be the caufe of cohefion, e44 ladicity, gravity, eledlricity, magnetifm, &c. in 44 the following manner: 1. As the rays of light, 44 when refiefted, do not touch the folid parts of bo44 dies, but are reflefted a little before they reach 44 them, it is plain that the aether not only fills the 44 pores of bodies, but likewife floats upon their fur44 faces ; and hence it becomes the caufe of attradlion 44 andrepulfion.— 2. All metals, and ineladic fluids, 44 are non-ele&rics ; on the other hand, all folid bo44 dies, metals excepted, are eleftrics, i. e. proper for 44 accumulating aether. But aether, thus accumulated 44 in fuch a variety of bodies, may produce various 44 motions in the parts of thefe bodies, without indu44 cing any change in the bodies themfelves. Hence 44 aether, with fome variations in its modification, is 44 fufficient to account for all the phaenomena of elec44 tricity. 3. As iron, by accumulating aether around 44 it, exhibits all the wonders -of magnetifm ; fo this 44 magnetical aether is more analogous to the nervous 44 aether of animals than any-other kind of it. For, 44 as the magnetical aether paffes along iron without 44 changing any part of the iron ; fo the nervous aether, 44 in like manner, paffes along the medullary fubdance 44 of the nerves, and excites motion in any part; that is 44 continuous with them, without inducing any change 44 in the nerves.— 4. The irritability and life of 44 plants, which very much refemble thofe in animals, 44 cannot be explained by any ineladic caufe, and 44 mud therefore be attributed to an astherial one. 44 Ladly, As the common asther is differently modi44 filed in each of the fubdances above taken notice 44 of, and alfo produces various motions or effects pe44 culiar to each, it likewife varies and has fome pe44 culiar qualities when refiding in animal bodies ; fo 44 that the nervous or animal aether is not exactly the 44 fame, but differs in fome refpefts from thofe fpecies 44 of aether which give rife to cohefion, gravity, magnetifm, electricity,” &c. Having thus explained the nature and qualities of sether, our author darts a very important quedion, viz. 44 Whence is aether derived ? and whether does it leave any body after .haying once 44got poffeflion of it ?” In44 anfwer to this,' he ohferves, That certain bodies 44 have the power of 'collecting the electrical matter 44 from every circumjacent body, and of accumula44 ting it in their pores and on their furfaces, but do 44 not differ it again to tranfinigrate into any other 44 body. There are other fubdances of an oppofite 44 nature, which do not accumulate the eleCtric mat44 ter, butindantly allow it to pafs into others, unlefs 44 44 prohibited by an ele&ric. Hence,” fays he, no44 thing more is neceffary for fubdances of the former 44 kind, but to be in fuch circumdances as allow them In the fame 44 to accumulate the ele&ric matter. 44 44 manner,” proceeds our author, the nervous sether, which is diffufed through every part of 44nature, flows