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XLIII. Intelligence and Miscellaneous Articles. 



ON CENTRAL FORCES AND THE CONSERVATION OF ENERGY. 

 To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 IVTR. BBOWNE asserts that my criticism of his paper in the 

 ■*■*-*■ January number of the Philosophical Magazine was not jus- 

 tified, on the ground that he had shown on page 38 that there could 

 not, consistently with the conservation of energy, be a component 

 at right angles to the straight line joining the two particles. Now 

 the assertion that such a component, if it exists, will produce a 

 rotation of B round A, which will increase B's kinetic energy, 

 and that this increase will go on for ever, is only necessarily true 

 if it can be shown that the component is not a function of ; for 

 if it be a function of 6 it will not necessarily tend to cause rotation 

 continuously in the same direction. I did not allude to this in my 

 communication to the February number, because in the argument 

 which I criticised no mention was made of the fact that the non- 

 existence of a component at right angles to the joining line must 

 be assumed before it can be shown that the component in that line 

 is a function of the distance only ; and therefore I could not tell 

 whether Mr. Browne considered this remark to justify his previous 

 argument, or to be justified by it. However, even if it be proved 

 that the component in the joining line is independent of 6, it does 

 not appear to follow that the component at right angles, if it exist, 

 is also independent of 0. I have the honour to remain, &c, 



G. W. VON TlJNZELMANN. 



ON THE REFRACTION-INDICES OF GASES AT HIGH PRESSURES. 

 BY J. CHAPPUIS AND CH. RIVIERE. 



The constancy of the refractive power of gases, assumed by Biot 

 and Arago after experiments in which the variation of the pressure 

 did not exceed 1 atmosphere, has not hitherto been verified. 



Since that period the problems stated by Arago respecting the 

 refraction-indices of gases have been the subject of important in- 

 vestigations ; but the physicists who have occupied themselves with 

 these questions have regarded them chiefly as astronomical, and 

 their aim has been to furnish the data which are indispensable for 

 the calculation of atmospheric refraction ; hence their experiments 

 have been confined within the limits of atmospheric pressures. 



The remarkable experiments of Andrews on the liquefaction of 

 carbonic acid led him to the observation of some interesting phe- 

 nomena produced in the gaseous mass at the moment of its change 

 of state. The well-known appearances described by him cannot 

 but be due to variations in the index of refraction of the gas. 

 Moreover the disappearance of the meniscus at what has been 

 called the critical temperature proves that at that instant the sub- 

 stance under experiment has only one index of refraction, while at 

 lower temperatures there are to be distinguished the index of the 

 liquid and the index of the gas. 



These facts appeared to us to give some interest to a study of 

 the indices of gases at high pressures. 



