188 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



of the air; second, that, however, a rise in temperature does 

 produce a slight but constant increase in the potential. 



OPTICAL PHENOMENA. 



Montigny gives a preliminary chapter of results of his ob- 

 servations on the Scintillations of the Stars. The first inter- 

 esting observation that he publishes is in the Bulletin of the 

 Royal Academy at Brussels, 1878, p. 157. It was first no- 

 ticed by Usher, 1788, at Dublin, that the stars scintillate re- 

 markably during and preceding an aurora. In 1840 Arago 

 says that Forbes and Neckar and himself agreed that the 

 stars never scintillate unless there is an aurora somewhere. 

 Montigny observed an especial increase of scintillation of 

 auroras April 5, 1870, and June 1, 1878. He also says that 

 the scintillation is connected with a lowering of temperature, 

 and that this cooling occurs simultaneously with auroras 

 and. scintillation, and that, finally, the cooling causes the 

 scintillation. In the second communication, in the Bulle- 

 tin, Brussels, vol. xlv., p. 391, he gives the results of Seven 

 Years' Observations with his Scintillometer on Fifteen Stars 

 as to Color, and finds that the red colors predominate during 

 dry weather, while the blue precedes rain. The memoir on 

 the Connection between Scintillation and Rain, etc. {Bulletin, 

 1878, p. 598), is received too late to allow of the extended 

 notice that it deserves. 



A memoir by Wild (St. Petersburg Bulletin, vol. xxi.,p. 312), 

 on the Photometric Determination of the Diftuse Light of the 

 Sky, gives the preliminary results of an investigation that 

 for many years has engaged his attention. The instrument 

 that he has invented and used for this purpose he designates 

 as the urano-photometer, and it seems to combine the feat- 

 ures of the photometers invented by Arago, Hirn, Wild, and 

 Zollner. A disk of ground glass illumined by the sun af- 

 fords an artificial standard light, whose whiteness is turned 

 to the required shade of blue by receiving it through a quartz 

 plate and polarizing apparatus. Wild finds (1) the color of 

 the diffuse sunlight, as we proceed from the sun northward on 

 a vertical circle, changes gradually from the red to the violet 

 end of the spectrum, and at a distance of 80 from the sun is 

 nearly between Fraunhofer's lines C and D, or at the wave- 

 length 0.000G28 meter; from here onward to the horizon the 



