SCIENCE. 



459 



opposes its centripetal force, from perihelion to aphelion, 

 and because at aphelion, the tangent of its orbit, is at right 

 angles with its radius vector, and from aphelion to peri- 

 helion the angle between the tangent and radius vector is 

 acute, therefore, the inertia of the planet co-operates with 

 the centrifugal force from aphelion to perihelion. 



Hence, inertia, in conjunction with the centripetal 

 force, is sufficient in all cases of elliptic motion, to bring 

 back the planet from aphelion to perihelion. 



Again, the writer says, (p. 407) "the degree of ellipticity 

 of each planetary orbit is due to the inclination of its 

 axis." That the reader may judge how much weight 

 should be allowed the author's statement, let this state- 

 ment be compared with known facts. 



The eccentricity of the earth's orbit is .0167922; that 

 of Venus is .0068618. The inclination of the earth's axis 

 is about 23^° ; that of Venus 75 . That is, the inclina- 

 tion of the earth's axis to its orbit is less than one-third 

 that of Venus ; whereas, the eccentricity of the earth's 

 orbit is more than twice that of Venus. 



The author's statement, therefore, is not only not sup- 

 ported by the facts, but is in conflict with the facts. 



J. E. Hendricks. 



Des Moines, Sept. 3, 1881. 



To the Editor of " Science ":— 



The prevailing scientific ideas of any period are re- 

 garded by the common people, and even by the scientists 

 of that period as indubitable facts, without due examina- 

 tion of their origin or their foundation. But further 

 thought and observation often compel a reluctant retreat 

 therefrom. Thus present conceptions have all the weight 

 of perfect truth. We call them "facts." 



The rapid discoveries of the present age, and the un- 

 precedented freedom of thought are disturbing all theories 

 that are not well founded. The new law of Conservation 

 of Force will cause the final destruction of every theory 

 that is not in harmony with it. The paper upon the 

 "Great Primordial Force " was but an effort to bring the 

 explanation of the physical forces into consistency with 

 that all-governing law. 



That the paper should give rise to such questions as 

 those proposed by our critic was most natural, and we 

 shall endeavor to answer them in the same candid spirit 

 in which they were asked. 



1. Bodies fall by force of gravitation. Resistance to 

 such fall of course produces light and heat, precisely as 

 resistance to the motion of the electrical current produces 

 the same. If we admit that the electrical current is con- 

 vertible into these forms, by parity of reasoning, so is 

 gravity. 



2. The relations of matter and force seem adequa'ely 

 set forth in the paragraph referred to. (See " SCIENCE," 

 p. 405.) Electricity, which in its tenuity pervades all 

 matter, is abundantly demonstrated to be itself matter in 

 varied form, as in the thunderbolt, the fire ball, and in 

 the St. Elnios fire. 



3 and 4. The only rational explanation, whether to us 

 satisfactory or unsatisfactory, of the origin of force, is 

 found in the hypothesis and admission of already existing 

 force, the primum mobile. Helmholtz says, that a 

 body set in motion around the sun in vacuous space, and 

 with a certain velocity will continue to move with the 

 same velocity to all eternity. It is sufficient for us to 

 know that the motion is, and the magnetism is, and thus 

 we have the " celestial armatures " already in revolution, 

 — the effects of which it is for us to observe. To us the 

 effects are, and are called, the "physical forces." 



Our critic is disturbed by our questioning of the dogma 

 that " gravity acts inversely as the square of the distance," 

 — on the ground that if that force is weakened by the 

 earth's being removed to aphelion, it could not again 

 bring back the body to perihelion. We re-affirm Fara- 

 day's position ; " The received idea of gravity appears 



to me to ignore entirely the principle of the conservation 

 of force, and by the terms of its definition, if taken in an 

 absolute sense, ' varying inversely as the square of the 

 distance ' to be in direct opposition to it." But we would 

 not rest the assertion upon any great name. It is evident 

 that inertia can " bring back " nothing, that inertia, or 

 momentum, or centrifugal force, or whatever other ex- 

 pression is used, may effect only motion in a straight line. 

 Momentum, (which evidently is what the critic means by 

 "inertia,") has no tendency towards circular motion. It 

 is attraction, gravity, centripetal force alone that draws, 

 or " brings back," and if that force is weakened, how can 

 it make itself stronger? If once diminished (as the prin- 

 ciple, " gravity acts inversely as the square of the distance " 

 necessitates,) then the opposite force has the balance of 

 power, has destroyed the equilibrium, and except some 

 favoring force steps in to restore the lost ground, momen- 

 tum, (" inertia ") must forever send it farther and farther 

 into space. 



Finally, our critic in order to show that the electrical 

 theory, which makes the inclination of a planet's axis to 

 govern the ellipticity of its orbit, is not true to fact, 

 adduces the instance of Venus. This asserted "fact" (?) 

 that Venus' axis has an inclination of 75 , is wholly un- 

 founded, Astronomers to-day are not so ready to assert 

 it. The dazzling brilliancy of this planet prevents any 

 positive disclosures as to the period of its daily revolution, 

 to say nothing of the more delicate and difficult deter- 

 mination of the inclination of its axis. 



Our distinguished astronomer NEWCOMBsays: — The 

 latest physical observations on Venus, with which I am 

 acquainted are those of Or. Vogel, " Bothkamp Obser- 

 vations, 1873." The result to which these observations 

 point is that the atmosphere of Venus is filled with clouds 

 so dense that the solid portion of the planet cannot be 

 seen, and no time of rotation can be determined." Her- 

 SCHEL said that he was never able to see any permanent 

 markings on Venus, — but it is only by such markings 

 that these determinations are made. 



H. Raymond Rogers, M. D. 



Dunkirk, N. Y. 



MEDICAL CONGRESS NOTES. 

 (London, 1881.) 



At the close of Professor Huxley's address, Mr. M^c- 

 Cormac followed with a statement, the most important 

 items of which were that the number of members 

 amounted to 3,210; that the sections had heid 11 meet- 

 ings, extending over 293 hours ; that there had been de- 

 livered 464 written papers and 360 oral addresses. The 

 attendance at the sections had been large, and had not 

 shown signs of falling off even quite to the close. The 

 museum was referred to as a great success, and the de- 

 monstrations of living patients had been attended by 

 crowds each morning. 



endorsing vivisection. 



Sir James Paget then presented the following resolu- 

 tion forwarded by Professor M. Foster, from the Physio- 

 logical Section : " That this Congress records its convic- 

 tion that experiments on living animals have proved of 

 the utmost service to medicine in the past, and are indis- 

 pensable for its future progress ; that, accordingly, while 

 strongly deprecating the infliction of unnecessary pain, it 

 is of opinion that, in the interest of men and animals, it 

 is not desirable to restrict competent persons in the per- 

 formance of such experiments." Pointing out that it 

 was impossible to discuss such a resolution then, the 

 President asked those who were opposed to it to record 

 their names and votes at the close of the meeting. The 

 resolution was then adopted with loud cheers, and no 

 hand was held up in opposition to it. 



