414 Intelligence and Miscellaneous Articles, 



of the inductive force must contribute a certain share to the decrease 

 of magnetism ascertained during the heating (4), and to the increase 

 ascertained during the cooliug (5); and the same variation may also 

 explain other facts, which I propose to discuss in a sequel to the 

 present memoir. — Comptcs Rendus de V Academic des Sciences, vol. 

 lxxxii. pp. 685-688. 



PRELIMINARY NOTE ON PHOTOGRAPHING THE LEAST-REFRACTED 



PORTION OF THE SOLAR SPECTRUM. BY CAPT. W. DE W. ABNEY, 



R.E. 



Within the last two years there have been many attempts made 

 to photograph the least-refrangible rays of the spectrum ; and 

 though stated to have been accomplished by the elder Draper on a 

 daguerreotype plate in the early days of photography, yet there is 

 reason to believe that this was effected by the reversing action of 

 these rays on slightly exposed sensitive iodide of silver, and that 

 really no direct photographic impression had been obtained till Dr. 

 Vogel published an account of a method for effecting this object 

 in 1874. More recently, Capt. Waterhouse, of the Bengal Staff 

 Corps, has followed up Dr. Vogel's researches, and with a larger 

 share of success than the originator. Both these gentlemen have 

 had resort to aniline dyes of varying colour, using them with the pre- 

 servative to the plate ; and they state that the red end of the 

 spectrum is most sensitive when a red dye (naphthaline) or rosine 

 is employed, and propound generally that the rays that can be 

 photographed are dependent on the colour of the dyes employed : 

 that colour, and not the ingredient added to the sensitive silver 

 salt, is the essential. 



Lately I have had occasion to investigate the subject, and have 

 met with such good results that I desire to communicate a prelimi- 

 nary Note to the Society. I have carefully repeated the previous 

 experiments of Yogel and Waterhouse, and only attained partial 

 success with them, though there was sufficient evidence to show 

 that with the dyes the desired end would be attained. Looking 

 more carefully into the chemistry of the question, however, it struck 

 me that the same results might be obtained by other means than 

 colour ; and experiments were undertaken with a large series of 

 gum-resins and other oxidized hydrocarbons (added to ordinary 

 collodion), some colourless and some not. With every gum-resin 

 was obtained a considerable extension of the photographic spectrum 

 below the lines b ; and at length I procured a resin forming with 

 silver a perfectly white compound that seems to be capable of 

 taking an image far below the line A. At present, I find that the 

 longer the exposure given, the greater the length of the spectrum 

 impressed; and I believe that, with patience, a very large part of 

 the absorption-lines lying beyond that point may be registered, as 

 I have obtained impressions which are constant in each plate ex- 

 posed. The past winter has been of a most unsatisfactory nature 

 for this kind of work, and it is only at long intervals that I have 

 been enabled to catch the sun for this purpose. I am earnestly 



