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XV. Further considerations on the Existence of a Fourth Im- 

 ponderable. By John William Draper, M.D., Professor 

 of Chemistry in the University of New York*. 

 T N the Philosophical Magazine for December 184-2, 1 brought 

 ■*- forward several facts which had caused me to form the 

 opinion that the chemical rays of the older optical writers 

 constitute in reality a new imponderable substance, which 

 should be placed in the same rank with light, heat and elec- 

 tricity. To the views then given I propose, in this commu- 

 nication, to return again, and furnish further proof of their 

 correctness. An extended examination, which has occupied 

 me several years, has served to deepen my conviction of the 

 truth of this doctrine. 



Great changes in the fundamental theories of science ought 

 not to be lightly admitted. It was only after many years of 

 discussion and multitudes of experiments that the doctrine of 

 the unity of air was destroyed, and the theory of the intrinsic 

 differences of gaseous bodies received. This was unquestion- 

 ably the most important event that ever happened to che- 

 mistry. 



The imponderable principles are the true living forces of 

 chemistry. The circumstance that they do not exhibit the 

 property of weight is only an incidental affair, and ought never 

 to have been regarded as their leading characteristic; they 

 are the regulating forces by which ponderable matter is ar- 

 ranged and grouped. If, then, so great a change occurred 

 in chemistry on more exact views being obtained of its pneu- 

 matic department, what may not be expected from the discus- 

 sions which are arising on the nature of its great controlling 

 forces ? 



There is another point of view from which these investiga- 

 tions assume a deep interest. I have shown (Phil. Mag., 

 Sept. 1843) that by resorting to prismatic analysis in physio- 

 logical researches, very remarkable truths appear. The func- 

 tion of digestion, which is carried on during sunshine by the 

 leaves of plants, is under the control of the yellow ray. It is 

 this which causes the decomposition of carbonic acid, furnishes 

 solid food, and gives the green colour. In animals similar re- 

 sults are produced by the agency of a nervous system; and 

 not only so, but all the various operations connected with life 

 are conducted in the same way. There is one class of nerves 

 which gives action to the respiratory apparatus, and another 

 which controls digestion. There is one class which presides 

 over motion, another which is the recipient of sensation, a third 

 which originates all the processes of thought and intellectu- 

 ality. In the vegetable world the same idea is preserved, de- 

 * Communicated by the Author. 



