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LXXX. On a ?iew Imponderable Substance, and on a Class of 

 Chemical B,ays analogous to the Rays of Dark Heat. By 

 John William Draper, M.D., Professor of Chemistry in 

 the University of New York*. 



[With F igures, Plate I.] 



IN the Number of this Journal for September 1841, I have 

 pointed out several analogies which may be observed be- 

 tween the phsenomena of the chemical rays and those of ra- 

 diant heat. 



In this communication it is my intention to show still more 

 striking points of analogy, and also to direct the attention of 

 chemists to equally striking points of discordance. 



It will be seen from the remarkable facts detailed in this 

 paper, that we are now forced to recognize the existence of a 

 new imponderable agent, analogous in many of its properties 

 to light, heat, and electricity, yet differing as much from them 

 all as they do from one another. 



So far as chemical analogies can direct us there does not 

 appear any thing unphilosophical in the supposition of the 

 existence of many imponderable agents analogous to those 

 already known. The progress of science has indeed tended 

 in different directions in the cases of the imponderable and 

 ponderable bodies. Among the former, we have successively 

 seen the agents that are concerned in galvanic phenomena 

 and those of magnetism merged into electricity; but the 

 ponderable bodies, especially those of a metallic kind, have 

 greatly increased in number, though so far as their more ob- 

 vious physical properties are concerned, the differences of 

 many are almost undistinguishable. We have thus found it 

 necessary to invert the maxims of the early cultivators of che- 

 mistry, who extended the number of aethereal agents very 

 greatly, and believed that all metals and other ponderable prin- 

 ciples were modifications of one or two primordial and ele- 

 mentary forms. 



Centuries ago it was discovered that the sun's light had 

 the property of effecting chemical changes in bodies, and it 

 is stated that Scheele first noticed that this property was 

 mainly due to the violet rays. Seebeck observed, that chlo- 

 ride of silver, exposed to the spectrum, varied its colour with 

 the colour of the space in which it was held, and during the 

 present century a very large amount of new observations has 

 been accumulated. A new art, Photography, has come into 

 existence. 



The general supposition that obtains is, that the effects in 

 question are due to the rays of light ; hence all the words that 

 * Communicated by the Author. 



