50 Dr. Draper on Mr. Hunt's Researches on Light. 



should set their faces against these things. Twice in the 

 brief history of photography have these unpleasant occurrences 

 happened. Egerton published a treatise* in which the names 

 of Sir J. Herschel and Mr. Hunt were scarcely to be seen. 



The air of vanity and the curious errors which pervade this 

 book will impose on some and amuse others. But there is 

 one point to which I wish particularly to direct the attention 

 of your readers. As is well known to them, 1 have ever since 

 1842, written from time to time papers to prove the existence 

 of a fourth imponderable ; [ gave it a name, and have incor- 

 porated that name prominently in all my writings. Before me 

 no person had ever hinted that the well-known chemical rays 

 constituted a new imponderable, which was entitled to the 

 same rank as light, heat, and electricity. It is now too late 

 for any attempt to be made to deprive me of the right of pro- 

 prietorship over that capital fact. Yet Mr. Hunt^ in this hook, 

 actually appropriates it to himself, aiid gives the fourth impon- 

 derable the name o/"Energia. 



Had Mr. Hunt represented his treatise as giving his own 

 researches and opinions, it would have answered to its name ; 

 but, when he sets it forth as containing all that is known up 

 to the present time, he does a great injustice to almost every 

 one who has written on these matters. For myself, of the dif- 

 ferent facts I have published in this and other Journals, nine- 

 tenths are not so much as alluded to. A person who should 

 content himself with the information here given, would scarcely 

 have an idea of the present advances of the science, and would 

 mistake it for a heterogeneous collection of isolated facts. 



I hope such of your readers as take an interest in photo- 

 graphy, will look at that chapter which commences on the 

 259th page, and also at the concluding paragraph of the pre- 

 ceding one. Let me ask them, whether they would not infer 

 that the idea of the existence of a fourth imponderable was 

 now in 184-4 brought forward for the first time by Mr. H. 

 Then let them turn to the papers written by me in 1842, and 

 notice the same arguments used for the same purpose, and 

 this very doctrine emphatically set forth (Phil. Mag. Dec. 

 1842). If the original observer of facts, — the original pro- 

 pounder of an important idea, is to have his rights thus unce- 

 remoniously put aside (and should the world of science be 

 led to countenance the proceeding), there is an end of every 

 inducement to philosophical pursuits. 



The chemical rays were discovered in the last century. 

 The idea that they constitute a fourth imponderable of the 

 same rank as light, heat, and electricity, belongs to me. That 

 * A translation of Lerebours's Treatise, with additions. 



