Mr. Earnshaw's Reply to Prof. Kelland's Defence. 437 



of film as at the commencement, about double the time is re- 

 quired. 



The third cause of error may be avoided by operating with 

 vapours of about the same force. In those described, the 

 average time employed in passing to the maximum was ge- 

 nerally about half an hour ; if that were not taken into consi- 

 deration, different results might be obtained. 



In regard to chlorine, there exists another cause of compli- 

 cation, the affinity which it possesses for water ; for when dis- 

 engaged in the ordinary manner, chlorine carries with it a 

 certain quantity of water which may very much alter the re- 

 sults of the experiment. 

 No. 1, St. Mary Abbot's Terrace, Kensington. 

 [To be continued.] 



LXXVII. Reply to Professor Kelland's Defence of the New- 

 tonian Law of Molecular Action. By S. Earnshaw, M.A. 



Cambridge *. 



P 



ROFESSOR Kelland's defence of the extension of New- 

 ton's law of force to molecular action consists of a critique 

 upon my memoir " On the Nature of Molecular Forces ;" 

 and of a reply to my letter which appeared in your Magazine 

 for July (pres. vol. p. 46). I shall therefore for the sake of 

 precision divide what I have to say in answer to his remarks 

 into two corresponding heads. 



1 . With respect to the critique on my memoir, it is evident 

 that it has been written by the Professor under the notion that 

 my investigations have supposed each particle of the medium, 

 except the one for which the forces are calculated, to be in 

 their respective equilibrium positions. I gather this from the 

 repeated charge he brings against me of drawing dynamical 

 inferences from a statical investigation. Will the Professor 

 point out what step, in that part of my paper which is written 

 against Newton's law, requires that the particles of the me- 

 dium should be in their equilibrium positions ? With the ex- 

 ception of the last article, where it is expressly stated that the 

 particles are in equilibrium, my paper is an investigation of 

 the properties of a vibrating medium, i. e. a medium in a state 

 of vibration. At any instant during the motion of the medium 

 I fix upon a particle and investigate the properties of the forces 

 which urge it at that moment ; the other particles meanwhile 

 are supposed to be in the positions which as particles in a 

 state of vibration they had at the instant fixed upon. [Let 



* Communicated by the Author. 



