The Invisible Solar and Lunar Spectrum. 505 



a slight visible discharge from the edge of the foil on the back 

 of the plate, and probably therefore the same from that on 

 the film to which the edge-marking may be due. There was 

 also on the plate much blotchy marking, apparently corre- 

 sponding to the wrinkling of the foil in contact with the film. 



"With a piece of gutta-percha tissue between the stencil- 

 plate foil and the film, the result was similar, only the line 

 round the edges was narrower and the blotching less marked, 

 hence the initials came out more distinctly. When four thick- 

 nesses of gutta-percha were interposed, there appeared only 

 blotchy markings on the part under the foil. 



These results would go to show that actual disruptive dis- 

 charge over or in the film is not needed to produce an effect 

 visible on development, but that the figures are produced 

 partly at least by direct electric action on the sensitive film 

 without the intervention of a visibly luminous action, or 

 what would be usually understood as a purely photo-chemical 

 cause. Possibly further investigation may show that we have 

 here a new kind of experimental evidence on the relation of 

 electricity to light. 



I may add that it is necessary, especially in the experiments 

 with the terminals on the back of the plate, to use rather 

 sensitive plates ; " 60 times " plates do very well, while slow 

 plates give imperfect figures in all cases and show almost 

 nothing with the terminals on the back. 



LIX, The Invisible Solar and Lunar Spectrum. 

 By S. P. L ANGLE Y*. 



THE following investigation has been made from studies 

 at the Allegheny Observatory ; but it is proper to state 

 that the provision of the very special apparatus used is due to 

 the liberality of a citizen of Pittsburgh, who has desired that 

 his name should not be mentioned. 



This paper is an abstract of a forthcoming memoir, which 

 will eventually appear in the fourth volume of the publications 

 of the United States National Academy of Sciences, to which 

 the reader is referred for fuller details. 



* Communicated "by the Author, to whom we are likewise indebted for 

 the cliches. 



As the writer has already presented to the National Academy a 

 memoir Tread October 17. 1884, Memoirs Nat. Acad, of Sci., vol. iii.) 

 on the heat of the moon, in which he spoke of investigations still in 

 progress on it, it should be said that these are not yet published, and that 

 they are only j^iven here so far as is necessary in explanation of certain 

 anomalies in the infra-red solar-heat spectrum, which forms the principal 

 subject of the present paper. 



