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bodies which conduct it. This ingenious conjecture, however, ougit' to derive some support from facts; we wish to learn, that some trials have been made, proving that the alkaline air in this experiment is dephlogisticated; and, far.ther, that the increase is not fo great, when the shock is conveyed through conductors, which cannot be supposed to lose their phlogiiton : when we are satisfied in these particulars, we fall eagerly wish to know the laient sources of the earth and the acid, requisite, agreeable to the Doctor's theory, for this appearance.
Sect. XXi1). treats of the volatility of the mercury, which is in contact with the vitriolic acid air, when the electric exploficn, is conveyed through it. This, like the former section, is calculated to surprise as well as to entertain us.
The remainder of this volume contains a variety of interesting norelties, but they are of that miscellaneous nature which will not allow us to give any general view of them. In Iris miscellaneous 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 second rupture takes place close to the cement, excepting where the glass is very thick. His fad experience, we acknowledge, as he describes it in this section, is very great; but a single fact, in which we have known a thin green glass phiai, after undergoing the process he describes, break at a great distance from the cement, is sufficient to convince us that the Doctor is wrong
in making the position fo general.- Towards the conclusion 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 subjoined to each general position, 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, some of the most instructive and entertaining; we apprehend, the mode he has observed in part seventh, vol. ij. of his History of Electricity, would be of great use in such cases.
· Dr. Priestley, we hope, will ascribe the freedom of our strictures on several parts of the excellent work before us, to a vanity, which is Hattered by discovering a few trifing errors amidst that crowd of excellencies, by which he commands our praise and admiration. If the encouragement he received were adequate to our wishes, he would indeed be most amply rewarded : he would proceed, in the new philosophical world which he has discovered, without meeting any obstructions, N 4
but such as must neceffarily refult from the novelty and variety of his enquiries.
Physiological Disquisitions ; or, Discourses on the Natural Philo
fophy of the Elements. 1. On Matter. 2. On Motion. 3. On the Elements. 4. On Fire. 5. On Air. 6. On Sound and Mufic. 7. On Fofil Bodies. 8. On Physical Geography, or the Natural History of the Earth. 9. On the Weather. By W. Jones, F. R. S. Rector of Pafton in Northamptonshire, and Author of
of an Elay on the first Principles of Natural Philosophy. 470. il. Is. in boards. Robinson. To this work the author has prefixed a handsome dedica
tion, but rather too long for the fashion, to the secretary at war; and the convenience of the reader is happily consulted in a new sort of index to all the figures in the copperplates, explaining briefly the subject 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 same subject, which was preparatory to the present work. The grand principle which he has in view is to exemplify and prove the action of the elements or one another, that all natural philosophy may be reduced to one simple and universal law; and we muit acknowledge that this principle, as the author has pursued it, leads us to a new prospest of the economy of nature. There is such a variety of matter in this work, that we cannot enter far into particu. lars, otherwise we would set down the author's arguments, which are adduced to thew the insufficiency of the established demonstration of a vacuum, in pages vi. and vii. of the In. troduction. He observes, that there are four diftinct forms of philosophy, which must be applied to by those who would understand natural philosophy in its proper extent; viz. the mythological, systematical, experimental, and facred ; of all which, with their excellencies and their defects, he has given a particular account, and has made his 'use of them in the course of the work. Speaking of the improved state of experimental philosophy, he has the following reflection, 1 have often indulged a wish that I could exhibit to the wise men and heroes of ancient times some 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 see the experiments upon the Warren at Woolwich, together with all the evolutions and firings of a modern battalion ; I would shew to Julius Cæsar,
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 observes, that his work is properly physiological, and its demonftrations rather from plain facts, accommodated to all capacities, than from abstruse reasonings ; whence all persons 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 discourse 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 transgress the bounds he had at first allotted to that branch. Musical philosophers are scarce; of electrical philosophers there is great plenty; and therefore, it is probable, the author has disappointed more than he has gratified by the subftitution of music for electri. city; but we hope it will not be long before his original de. sign will be accomplished; as many will with to fee how electricity will confirm his principle. In this introduction many things are advanced concerning the alliance between philofophy and divinity, and some celebrated writings are cited as authorities; amongst the rest an extraordinary character is given of our ancient Englih philosopher, commonly known by the name of Friar Bacon. Some strictures are also added on the abuse of natural philofophy, by Voltaire and others.
As a specimen of the author's style and manner, we shall present the reader with the last paragraph of his introduion, in the whole of which the learned reader will find many interesting observations.- I have now, as I hope, fully explained the considerations which prevailed with me to write on natural philosophy; and I can sincerely 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 desire him to remember, that my whole fcheme should be taken together, and that this book is but a part of it. When I first looked forward upon the plan, I had 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 some better hand to execute ; and were I to detain a work of fo much difficulty, and comprehending such a variety of subjects as will be found in it, till I could approve it, and be satisfied that I had done what I might and ought to have done, it would never come abroad. I must therefore hope to correct some things by farther examination ; and I shall never be ashamed to improve what I publish, by means of such hints as friendly information, or even hostile criticism itself, shall hereafter throw in my'way. If some should neglect my phiJosophical writings, either on the just ground of their own fuperior knowledge, or from lower motives of vanity, envy, or interest; I know that every vauthor must 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, suggests 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 striking, fo intimately in terwoven 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 some other; with abilities to defend what shall have been rightly done in this great subject, and to improve it by their own more successful labours."
In the discourse on Matter, he confiders the different forms in which the elementary parts of bodies appear, and how the properties of bodies may arise from the configuration of their parts. Divisibility of matter-is thewn to be not infinite, but only indefinite; inasmuch as matter must be supposed to confist of units as the rudiments of boilies. All the primary properties of matter are reduced to barines and mobility; and many facts are introduced to illofrate the fecondary properties of bodies from their compositions and decompositions. The continuity of inatter is sewn to be necesary to many of its effects ; and discontinuous matter is said to aci by means of other matter co-cperating with it. It is also fewn how bodies may increase in bulk, and yet preserve their continuity. Atoms, in a state of separation, do not gravitate fpecifically, as when in masses, and as all matter has not a tendency toward a centre, gravity is not essential to matter. larity of atoms is explained and exemplified, and the visibility of matter supposed to be a confequence of its concreting into masses. To those physical observations on matter the author has fubjcined its mythological history, in the fabulous characters of Saturn and Proteks, and the Satyrs, together with the Pythagorean philofophy, founded on the transformations of matter, and the phenomena of generation and corruption in the economy of nature.
The discourse on Motion is chiefly employed in the investigation of its causes. As reatter has no active properties of its own, but by its nature indifferent to motion, its motion must criginate from, and be preserved by the influence of invisible power : but this power does not act without the intervention of fecond causes, of which there is a chain, each depending
on the other, and all subordinate to the Creator. Nature is to be considered as a connected system, because nothing can be learned of matter by considering it abstractedly. This reasoning is illustrated 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 constantly by the causes of life ; fo motion by the causes of motion. To say that the body lives to-day, because it lived yesterday, is to give as good a reason for the continuance of life, as Descartes gives for the continuance of motion. The case of a moving pendulum is very subtile, yet supposed to be reducible to the general rule. Some causes are known to the bodily senses; 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 Auids is both progreslive and vibratory, admitting of great variety in the same fluid, without interruption to itself. All motion must be in the direction of its cause; whence all attraction, commonly so called, must resolve itself into impulse. We fay of a plaster 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 plaster. When a body retains its motion without diminution, it is moved by a cause which would renew the motion if it were fopt: hence projection cannot he admitted as a principle of motion in nature ; it is a principle only of that motion which is violent and artificial. rallel is here introduced, to fhew that the planetary motions may be effected by very gentle forces, acting insensibly. All motions are to be referred to corporeal causes ; philosophy cannot proceed without them : all experiments on the elements tend to fhew how some matter produces changes in other matter : nothing else is intelligible. The principle of a circulation in nature is pursued at large, and contended for as a folution of many difficulties in nature, not otherwise to be accounted for. Motion in a plenum is possible or impoflible under different circumstances which should be distinguished. Resistance is no argument against the admission of impelling forces, for the cause of motion, whatever it may be, raré or dense, can never be said to resist the motion which it causes.
The matter of this disquisition, 'which, however abstruse, is necessary to be introduced into philofophy, is made more plain in what the author calls a' recapitulation, from which a reader may soon see what it contains, and judge of its merits.