[ 270 J 
XLIX. Some Experiments and Remarks on the Changes 
which Bodies are capable of undergoing in Darkness, and on 
the Agent producing these Changes. By Roperr Hunt, 
Secretary to the Royal Cornwall Polytechnic Society. 
To the Editors of the Philosophical Magazine and Journal. 
GENTLEMEN, 4 
HE communications which have appeared in your Jour- 
nal from Professor Draper of New York, I have studied 
with the greatest interest, seeing in him an able ane’ industri- 
ous inquirer in that path of science to which I have myself 
directed some attention. In the pages of the Philosophical 
Magazines for November and December 1842 and March 
1843, are three papers by Dr. Draper, in which he seeks to 
explain many of the phenomena with which the art of photo- 
graphy has brought us acquainted, and those still more mys- 
terious effects to which the labours of M. Moser* have called 
general attention. With the first of these papers I have at 
present little to do, having in my essay on Thermography, 
which you did me the honour to publish in your Magazine 
for December, acknowledged the priority of Dr. Draper’s 
observations on Latent Light. I would however notice, in 
reference to Sir John Herschel’s valuable remarks on the 
Daguerreotype which accompanied that paper, which you 
printed in February, that your Magazine for April 1840 con- 
tains a communication on “The Chemical Action of the 
Solar Spectrum,” accompanied by a drawing, from me, which 
will show that I have a prior and very distinct claim to the 
prismatic analysis of the Daguerreotype photograph, which 
Sir John Herschel has, with characteristic readiness, acknow- 
ledged in a note with which he has honoured me, dated Fe- 
bruary 17th. Professor Draper’s paper ‘“‘ On a New Impon- 
derable Substance, and on a Class of Chemical Rays analo- 
gous to the Rays of Dark Heat,” and also that “On the 
rapid Detithonizing Power of certain Gases and Vapours,” 
&c., claim our especial attention. The object of these com- 
munications is to prove that the property of effecting chemical 
change, which has been considered due to the rays of Lieut, 
ought to be attributed to a ‘new imponderable substance,” 
which Dr. Draper proposes to call Tiruonicrty. Although 
many of the very remarkable effects which I have observed 
have frequently led me to consider seriously the propriety of 
separating the rays by which they were produced from Liaur 
* See translations of M. Moser’s treatises in Taylor’s Scientific Memoirs, 
Part XI.—Some notices relating to the subject will be found among the 
Miscellaneous articles in our present Number.—Ep, 
