The active Agent in producing Photographs in the Dark. 409 



the other elements have also been excessive as compared with their 

 average amounts. 



Thus, the mean distance of the meteors occupying segment A of the 

 stream has been undergoing so much extension, that the meteors will at 

 the end of the revolution find themselves with a periodic time longer 

 by one-third of a year an amount of change which must largely affect 

 their future history, unless this great perturbation is compensated by 

 what happens elsewhere or at other times. 



At the epoch 1899, November 15, the longitude of the node will be 

 53 41''7, a position which the earth will reach on 1899, November 15d. 

 18h. It is probable, therefore, that the middle of the shower of the 

 present year (1899) will occur nearly at this time, since segment A in 

 the stream, for which our calculations have been made, is situated in 

 the stream less than three months' journey of the meteors behind 

 the segment which the earth will encounter next November, and which 

 we may call segment B. This conclusion, however, rests on two 

 assumptions : (1) That segments A and B were, in 1866, moving in 

 orbits that did not much differ ; (2) That the perturbations which seg- 

 ments A and B have since suffered have not much differed. Both 

 assumptions are probable, but unfortunately neither is certain ; so that 

 the prediction can only be offered with reservation. If the shower 

 occurs at the time anticipated, it will be visible from both Europe and 

 America. 



" On Hydrogen Peroxide as the active Agent in producing Pictures 

 on a Photographic Plate in the Dark." By W. J. RUSSELL, 

 Ph.D., V.P.R.S. Received February 18, Bead March 2, 

 1899. 



In previous papers it has been shown that certain bodies are able, in 

 the dark, to act on a photographic plate and produce a picture. The 

 purpose of the present communication is to show that in all the cases 

 which have been examined, and probably in all others of a similar 

 kind, the action which occurs is due to the presence of hydrogen per- 

 oxide. As a sensitive plate always contains moisture, and probably 

 would be inactive if quite dry, it does not seem possible to test the 

 truth of this statement by Jthe total exclusion of moisture ; there- 

 fore more indirect means have to be adopted. In the following paper 

 no attempt is made to explain the reactions which occur in the plate 

 itself ; that is a distinct question, and at present the object is to con- 

 sider the means by which these changes, whatever they may be, are 

 brought about. These changes are rendered visible by exactly the same 

 processes as those adopted for the development of an ordinary light 

 picture, Any of the ordinary photographic plates may be used in 



