bodies which conduct it. This ingenious conjecture, however, ought to derive fome fupport from facts; we wish to learn, that fome trials have been made, proving that the alkaline air in this experiment is dephlogisticated; and, farther, that the increase is not fo great, when the fhock is conveyed through conductors, which cannot be fuppofed to lofe their phlogiiton: when we are fatisfied in thefe particulars, we fhall eagerly with to know the latent fources of the earth and the acid, requifite, agreeable to the Doctor's theory, for this appearance. f Sect. XXII. treats of the volatility of the mercury, which is in contact with the vitriolic acid air, when the electric explofion is conveyed through it. This, like the former fection, is calculated to furprife as well as to entertain us. The remainder of this volume contains a variety of interefting novelties, but they are of that mifcellaneous nature which will not allow us to give any general view of them. In Iris mifcellaneous experiments in electricity, Dr. Priestley informs us, from his own experience, that in all instances, in which jars are over-charged, after they have been once cracked and then mended with cement, that the fecond rupture takes place clofe to the cement, excepting where the glafs is very thick. His fad experience, we acknowledge, as he defcribes it in this section, is very great; but a fingle fact, in which we have known a thin green glafs phial, after undergoing the procefs he defcribes, break at a great distance from the cement, is fufficient to convince us that the Doctor is wrong in making the pofition fo general.-Towards the conclufion of this volume we find a very valuable recapitulation of the principal facts contained in the preceding volumes. We think it might have been greatly improved, if the Doctor had fubjoined to each general pofition, a few of the leading experiments which evince and confirm it. We have heard many perfons complain, that when they wish to repeat his experiments they know not where to begin, or where to find, fome of the most inftructive and entertaining; we apprehend, the mode he has observed in part seventh, vol. ii. of his History of Electricity, would be of great use in such cases. Dr. Priestley, we hope, will afcribe the freedom of our ftrictures on feveral parts of the excellent work before us, to a vanity, which is flattered by difcovering a few trifling errors amidst that crowd of excellencies, by which he commands our praise and admiration., If the encouragement he received were adequate to our wifhes, he would indeed be most amply rewarded he would proceed, in the new philofophical world which he has difcovered, without meeting any obftructions, : N 4 but but fuch as must neceffarily refult from the novelty and variety of his enquiries. C. 3. Phyfiological Difquifitions; or, Difcourfes on the Natural Philo- Τ TO this work the author has prefixed a handfome dedication, but rather too long for the fashion, to the fecretary at war; and the convenience of the reader is happily confulted in a new fort of index to all the figures in the copperplates, explaining briefly the fubject and meaning of each. In an introduction he explains, at large, the nature and defign of his undertaking, and gives a particular account of a former publication on the fame fubject, which was preparatory to the prefent work. The grand principle which he has in view is to exemplify and prove the action of the elements on one another, that all natural philosophy may be reduced to one fimple and univerfal law; and we muit acknowledge that this principle, as the author has purfued it, leads us to a new prof pest of the œconomy of nature. There is fuch a variety of matter in this work, that we cannot enter far into particu lars, otherwife we would fet down the author's arguments, which are adduced to fhew the infufficiency of the established demonstration of a vacuum, in pages vi. and vii. of the Introduction. He obferves, that there are four diftinct forms of philofophy, which must be applied to by thofe who would underftand natural philofophy in its proper extent; viz. the mythological, fyftematical, experimental, and facred; of all which, with their excellencies and their defects, he has given a particular account, and has made his ufe of them in the course of the work. Speaking of the improved ftate of experimental philofophy, he has the following reflection, I have often indulged a wifh that I could exhibit to the wife mén and heroes of ancient times fome of those wonderful improvements, which are now fo familiar to us, but were totally unknown to them. I would give to Aristotle the electrical fhock; I would carry Alexander to fee the experiments upon the Warren at Woolwich, together with all the evolutions and firings of a modern battalion; I would fhew to Julius Cæfar, the the invader of Britain, an English man of war; and to Archimedes, a fire engine, and a reflecting telescope.' In defcribing the qualifications which he expects in his readers, he obferves, that his work is properly phyfiological, and its demonftrations rather from plain facts, accommodated to all capacities, than from abftrufe reasonings; whence all perfons of a liberal education may think themselves equal to the subject as he has treated it. An apology is made for deferring the publication of a difcourfe on electricity, intended as a part of this volume; which would have been too bulky with that addition; and the author's partiality to the philosophy of mufic, has tempted him to tranfgrefs the bounds he had at firft allotted to that branch. Mufical philofophers are scarce; of electrical philofophers there is great plenty; and therefore, it is probable, the author has disappointed more than he has gratified by the substitution of mufic for electricity; but we hope it will not be long before his original de fign will be accomplished; as many will wish to fee how electricity will confirm his principle. In this introduction many things are advanced concerning the alliance between philofophy and divinity, and fome celebrated writings are cited as authorities; amongst the reft an extraordinary character is given of our ancient English philofopher, commonly known by the name of Friar Bacon. Some strictures are alfo added on the abuse of natural philosophy, by Voltaire and others. As a fpecimen of the author's ftyle and manner, we shall present the reader with the last paragraph of his introdution, in the whole of which the learned reader will find many interesting obfervations. I have now, as I hope, fully explained the confiderations which prevailed with me to write. on natural philofophy; and I can fincerely affirm, that the work is rather a work of duty than of oftentation; to which, if the reader is inclined to do justice, I must defire him to remember, that my whole scheme should be taken together, and that this book is but a part of it. When I first looked forward upon the plan, I had a very different idea from that which presents itself to me, now I look back upon it. Had it appeared then as it does now, I should have left it for fome better hand to execute; and were I to detain a work of fo much difficulty, and comprehending fuch a variety of fubjects as will be found in it, till I could approve it, and be fatisfied that I had done what I might and ought to have done, it would never come abroad. I must therefore hope to correct fome things by farther examination; and I shall never be ashamed to improve what I publish, by means of fuch hints as friendly information, or even hoftile criticifm itself, fhall hereafter 1 > hereafter throw in my way. If fome fhould neglect my philofophical writings, either on the just ground of their own fuperior knowledge, or from lower motives of vanity, envy, or intereft; I know that every author muft commit his works to the times in which he writes, whether they are favourable or adverse to his undertaking; and when he has launched his veffel, he must leave it to the chance of the wind and the weather. My mind, however, fuggefts to me that this book will not be totally thrown afide and forgotten. The natural agency of the elements, for which I have pleaded, and, which I hope to carry farther, (however imperfectly) is fo reasonable, fo ftriking, fo intimately interwoven with the moft agreeable and interesting parts of literature, that it muft, when it comes to be better understood, find friends and favourers, either in this country, or fome other; with abilities to defend what fhall have been rightly done in this great fubject, and to improve it by their own more fuccefsful labours.' In the difcourfe on Matter, he confiders the different forms in which the elementary parts of bodies appear, and how the properties of bodies may arife from the configuration of their parts. Divifibility of matter is fhewn to be not infinite, but only indefinite; inafmuch as matter must be fuppofed to confift of units as the rudiments of bodies. All the primary properties of matter are reduced to hardness and mobility; and many facts are introduced to illuftrate the fecondary properties of bodies from their compofitions and decompofitions. The continuity of matter is fhewn to be neceffary to many of its effects; and difcontinuous matter is faid to act by means of other matter co-operating with it. It is alfo fhewn how bodies may increase in bulk, and yet preferve their continuity. Atems, in a state of feparation, do not gravitate fpecifically, as when in maffes, and as all matter has not a tendency toward a centre, gravity is not effential to matter. The polarity of atoms is explained and exemplified, and the vifibility of matter fuppofed to be a confequence of its concreting into mafles. To thefe phyfical obfervations on matter the author has fubjoined its mythological hiftory, in the fabulous characters of Saturn and Proteus, and the Satyrs, together with the Pythagorean philofophy, founded on the transformations. of matter, and the phænomena of generation and corruption in the economy of nature. The difcourfe on Motion is chiefly employed in the inveftigation of its causes. As matter has no active properties of its own, but by its nature indifferent to motion, its motion muft criginate from, and be preferved by the influence of invifible power: but this power does not act without the intervention of fecond caufes, of which there is a chain, each depending on on the other, and all fubordinate to the Creator. Nature is to be confidered as a connected fyftem, because nothing can be learned of matter by confidering it abftractedly. This reafoning is illuftrated from the relation between the limbs and the body in an animal. Bodies do not continue to move without the continuation of a moving force. Life is kept up conftantly by the caufes of life; fo motion by the caufes of motion. To fay that the body lives to-day, because it lived yesterday, is to give as good a reafon for the continuance of life, as Defcartes gives for the continuance of motion. The cafe of a moving pendulum is very fubtile, yet fupposed to be reducible to the general rule. Some caufes are known to the bodily fenfes; others are inferred by rational deduction from the laws of nature. In reviewing the different kinds of motion, he finds there is fuch a thing in nature as uniform motion in a right line; and that the motion of fluids is both progreffive and vibratory, admitting of great variety in the fame fluid, without interruption to itself. All motion must be in the direction of its caufe; whence all attraction, commonly fo called, must resolve itself into impulfe. We say of a plafter that it draws; but it cannot act in the direction of the effect; the force is from the vis vitæ propelling the fluids towards the plafter. When a body retains its motion without diminution, it is moved by a caufe which would re new the motion if it were ftopt: hence projection cannot be admitted as a principle of motion in nature; it is a principle only of that motion which is violent and artificial. A parallel is here introduced, to fhew that the planetary motions may be effected by very gentle forces, acting infenfibly. All motions are to be referred to corporeal caufes; philofophy cannot proceed without them: all experiments on the elements tend to fhew how fome matter produces changes in other matter: nothing elfe is intelligible. The principle of a circulation in nature is purfued at large, and contended for as a folution of many difficulties in nature, not otherwife to be accounted for. Motion in a plenum is poffible or impoffible under different circumftances which fhould be distinguished. Refistance is no argument against the admiffion of impelling forces, for the cause of motion, whatever it may be, rare or denfe, can never be faid to refift the motion which it causes. The matter of this difquifition, which, however abftrufe, is necessary to be introduced into philofophy, is made more plain in what the author calls a recapitulation, from which a reader may foon fee what it contains, and judge of its merits. [To be continued.] A Ge |