we cannot possibly discover, by the most exact observation of the polar star, that we have moved one inch!"

"The result of all observations made to ascertain this point has been, that the declinations of the fixed stars are every day in the year the same to a hair's breadth."

The author next discusses the theories of the atmosphere and the void spaces for planetary motion, which he maintains are refuted by decisive facts.

"Philosophers almost unvaryingly confound the elasticity or spring of the air, with its weight, and accordingly conclude, that a base of an inch square supports a column of air of fifteen pounds' weight; and by the same rule a middle-sized man is constantly pressed by about fifteen tons of air! Now, if that be true, how is it that a man exists, when, by mounting aloft in a balloon, until the barometer falls to ten or twelve inches, the pressure upon him, according to that rule, is suddenly reduced two-thirds, or about ten tons? When Mr. Robertson ascended at Hamburgh, a few years ago, it does not appear that he bursted, or even experienced any inconvenience whatever, from that cause, although the quicksilver in his barometer sunk as low as twelve inches and a half. Mr. Baldwin, too, when he ascended from Chester, in the year 1785, expressly mentions, that he experienced no inconvenience whatever; nor did Mr. Brydone when on the summit of Etna; the French on the Andes; or Dr. Heberden on the peak of Teneriffe. Others, I admit, are said to have experienced some difficulty of breathing when placed in elevated situations; but what does that prove? Not an increase of rarity, but the reverse. Dr. Fletcher, formerly an English envoy at the court of Russia, states, that when you there pass out of a warm room into a cold one, you will "sensibly feel your breath to wax stark and even stifling with the cold as you draw it in and out." The same sensation is mentioned by the French philosophers as felt by them at Tornea; in breathing they said their breasts seemed to be rent. The experience of every one proves that breathing is more difficult in frosty weather, when the density of the air is increased by cold, than in warm weather when it is rarefied by heat."

The state of the ocean, Mr. Prescot thinks an irresistible proof against the theories of the atmosphere, gravity, and earthly motion. Speaking of his opponents, he says,

"After having laboured hard, for about one hundred and forty years, to balance and compact the elementary parts of the system, they have been so astonishingly remiss, as to leave the ocean to the uncontrolled operation of three mighty forces, which would, in the first hour of the earth's motion, have completely swept it out of its bed, had not the Creator wisely ordered the matter otherwise."

*

*

*

*

*

"Those who have witnessed the effects of a storm of wind upon the ocean, which wind, even in a hurricane, is not supposed to move with a velocity greater than one hundred and forty miles in an hour, may easily conceive what would be the consequence to the ocean if the

earth moved through the firmament at the rate imagined by the Newtonians, namely, 68,000 miles an hour-500 times quicker than a hurricane!"

"The force which, according to Newton, causes a body, (suppose a bladder filled with water) near the surface of the earth, to fall about sixteen feet in one second of time, is that which presses the ocean to its bed that is the force of gravity. Now the power operating with that specific force upon the ocean, supposing the earth to move, is exactly crossed by another force on the equator above ninety times greater, namely the centrifugal, or rotatory motion of the earth, said to be upwards of 1500 feet in a second. Were the two forces equally balanced, the thing might appear plausible and go down tolerably well; but, as the matter is represented, nothing but a great miracle could prevent the water from flying off the surface of the earth, as it does off a potter's wheel, the moment the centrifugal motion of that wheel overbalances the gravity of the water lying upon its surface. But that is not all; we have still to notice the projectile force of the globe, which is calculated at 100,000 feet in a second; that is, 6000 times the force that presses the ocean to its bed, as aforesaid; which inconceivable velocity would, in eight minutes of time, completely separate the globe from the ocean; comparatively as a shallow plate, if filled with water, would, by a quick horizontal motion, instantly be emptied of its contents and leave them behind. Yet, under all the supposed influences of these powerful forces, operating in various directions, the ocean does not afford a single evidence of their actual existence."

The succeeding chapter is, in part, occupied with the investigation of the claim of the moderns to optical discoveries. Mr. Prescot is of opinion, that the ancients were not so ignorant of these matters as later opticians have imagined.

It is further conceived that the Newtonian maxims are impeached by the observations of Mr. Baldwin, in his aerial voyage from Chester, by the dark nature of earthly bodies, and by the evidence exhibited in the stars. At a certain elevation the earth appeared, as seen through the openings between the clouds,

"Of an obscure, greenish, or bluish hue, but the clouds were of a dazzling white. Moreover, instead of the water of the sea, rivers, ponds, and canals, appearing dark, as Cassini, above a hundred years ago, said it would, to any one, if he were placed at a great elevation above it; on the contrary, it appeared to Mr. Baldwin to be bright and shining; the pits, he said, were like spangles upon a dark ground. I recollect seeing that balloon when it penetrated the clouds; it did not appear like a luminous star, but the very reverse; and I therefore infer, that a globe of earth, at the same or any greater distance, would have had a similar dark appearance; or, rather, that at the distance of a few miles it would have totally disappeared, for want of the natural property of receiving and reflecting the beams of solar light."

The 10th Chapter is on the distances of the heavenly bodies;

and Mr. Prescot holds, that the methods proposed by astrono mers to ascertain them is inapplicable and useless. We give the following as one of his instances of objection:

.

"The refraction of the air, concerning which philosophers are entirely in the dark, as their own writings show,* renders this mathematical theory quite useless: besides which, may be mentioned the dif. ficulty of noting the exact time of the moon's passage through the zenith; the rapid change in her declination; the unavoidable inaccuracy of instruments and time-pieces, used in making observations, and even the liability, in nice observations of this kind, to be deceived by the eye itself. These are obstacles which no human art can surmount. Besides, the moon moves through an angular space equal to what they estimate the whole parallax to be, in less than four minutes of time."

Mr. Prescot possesses the advantage of detecting some inconsistencies in the calculations of his predecessors. Copernicus, and the astronomers of the present day, it appears, differ very widely on the point of the distance of the earth from the sun. Even Newton's computation is no great deal more than onehalf of that which is now maintained, and that of Copernicus is about th part! The following is a statement of the varieties of these astronomical opinions:

The accurate calculation of eclipses, and the transit of Venus, have been adduced as proofs of the accuracy of the present accredited system. But our indefatigable author refers to the writings of Ptolemy; the Arabian astronomers; Tycho Brahe, and others, to shew that the science of calcu lating eclipses was known some thousand years before computations were formed upon the hypothesis of the solar system, which he contends is of no real use in such calculations.

We have thus presented an analysis of the principal and most curious parts of this volume. We pledge ourselves to neither side of the question. We intend to examine Mr.

* It would be endless to notice the different opinions respecting both the terrestrial and the astronomic refractions which are to be met with in the writings of various authors on the subject; and it would be equally useless to notice all the tables of its quantity given by them, some of which differ very much from others.-Dr. Rees's New Cyclopædia, article Refraction.

Prescot's second book, in which, we understand, the subject is inore at large discussed; and, if we can detect any fallacy, we shall freely and fairly bring it forward; but the volume is of some magnitude, and the mathematical part will require time to investigate it. For the present, we trust, Mr. Prescot cannot complain of us. We have given him as impartial a hearing as possible. He must not expect us to be instantaneously converted. If truth be on his side, our notice will, in some degree, advance it; and, if his views be erroneous, they will sooner be detected, and the system he has attacked will be the more firmly established. We observe that the work has already acquired some share of public attention, and has been favourably mentioned by some of the periodical tribe. By one of these it is observed, that it is a fact which has greatly surprised some reflecting persons, that, during the forty years which passed from the publication of the Principia to his death, Newton never attempted to apply his own principles to the improvement of practical astronomy; nor, indeed, does it appear, that any of his friends or followers in England have ever constructed one original table from his principles !

Some of the fraternity of critics, as might be expected, have opposed the author. We think he has very needlessly provoked censure by the manner in which he has treated the memory of Sir Isaac Newton. Were we to concede to Mr. Prescot that Sir Isaac was mistaken in his theory of gravitation, it would not justify asperity of language against him. Sir Isaac was, no doubt, sincere in his philosophical opinions. Mr. Prescot denies the orthodoxy of Newton, but he does not prove the point; and, if he did so, there would still remain enough of merit to entitle him to respect both as a man and a philosopher. We think it neither consistent with that creed in which Mr. Prescot is evidently so firm, nor with the precepts of that sacred volume to which he so frequently and earnestly appeals, nor even with the calmness of sound philosophy, so vehemently to assail, as Mr. Prescot does, the motives and the labors of other men. Yet we ascribe his feelings to a wellmeant zeal, and an earnest belief in the truth of the system he advocates, and the importance of the principles with which they are connected. Perhaps, too, the author, in the inculcation of his doctrines, may have met with uncandid and ungentle treatment, and has felt himself justified (with the pen in his hand,) to retort the ridicule and throw back the asperity with which he was provoked. We think there is, at least, enough in these speculations, to entitle the author to a fair examination of his theory, and, if it be unfounded, there will surely be no great difficulty in refuting it.

476

The Medical Student's Guide; comprising Regulations for the Examination of Students at the Royal College of Surgeons, London, and at Apothecaries' Hall; Terms of the Surgical and Medical Practice of the Hospitals and Dispensaries in London; and of the various Lectures, with the Hours of Attendance; Pay of the Medical Department of the Army and Navy, and of the Hon. East India Company's Service. Also other Information interesting to the Medical Student. To which is added, a List of the most approved Elementary and Standard Medical Works.

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