34-8 Dr. Draper on certain Spectral Appearances 



my knowledge, so that the erroneousness of an equation af- 

 fects nothing but the equation itself. 



Mr. O'Brien's argument against the equations I have used, 

 viz. that 



CFr . 2 kdg\ 



is not zero, is good only on the hypothesis that g is not 

 measured along one of the axes. Had Mr. O'Brien read 

 my papers he would have seen that I have twenty times over 

 at least, given this expression a value which is not zero. But 

 when the direction of transmission in an isotrope medium is 

 under one of the axes, the expression is zero. And these are 

 the only circumstances in which I have used it as such ; your 

 readers will find my fundamental equations deduced in your 

 Magazine for May, 1837. I think they will see my views cor- 

 rectly stated there, and trust they will do me the justice to 

 examine them before they give credence to the following as- 

 sertions of Mr. O'Brien : — 



" And here I must enter a decided protest against all Pro- 

 fessor Kelland's reasoning on the subject of transverse and 

 normal vibrations." " Now this error in the fundamental 

 equations vitiates all his results, so far as they relate to the na- 

 ture of the vibrations and the velocity of propagation," &c. 

 " This error runs through all Professor Kelland's papers and 

 his f Theory of Heat,' so far as I have read them," &c. 



What could have dictated such expressions so utterly un- 

 grounded, I leave to the world to judge. 



In conclusion, Gentlemen, allow me to thank you for your 

 kindness in receiving my former communications, and to re- 

 quest that you will publish this in your forthcoming Number. 

 I have the honour to be your obliged Servant, 



P. Kelland. 



LXII. On certain Spectral Appearances, and on the discovery 

 of Latent Light. By J. W. Draper, M.D., Professor of 

 Chemistry in the University of New York. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 TF there be a thing in which I have a disinclination to en- 

 gage, it is controversy of a personal kind with scientific 

 fellow-labourers. But, as you well know, it ordinarily happens 

 that there is no other gain to philosophers beyond the mere 

 credit of their discoveries, they may be forgiven for reluc- 

 tantly endeavouring to secure this their only reward. 



I have recently returned from a long journey, undertaken 



