F. Cajori — Search for Solar X-Rays on Pike's Peak. 289 



Aet. XLII. — Search for Solar X-Rays on Pikers Peak ; by 

 Flokian Cajori. 



Experiments carried on by M. C. Lea* and others have 

 failed to show the presence of Rontgen rays in solar radiation. 

 If these rajs reach ns from tlie sun, their intensity must be 

 exceedingly feeble. The suggestion has been made that Ront- 

 gen rays may exist in sun-light, but are absorbed by the earth's 

 atmosphere. The fact that Lenard rays are stopped by onlj a 

 thin layer of air made it not improbable that Rontgen rays 

 might be stopped by a thick layer of it. On this hypothesis 

 a mountain top is the best locality to examine sun-light for the 

 new rays. The writer determined, moreover, to expose the 

 photographic plate to solar rays, not several hours, but several 

 weeks. 



During preliminary experiments made in Colorado Springs, 

 it was found that a sheet of aluminiam would allow certain 

 solar rays to pass through. These were not Rontgen rays, for 

 the reason that black paper placed between the aluminium and 

 the photographic plate seemed to cast as deep a shadow as did 

 a strip of iron. A different mode of exposing the plate was 

 necessary and a plan similar to Lea's was finally adopted. 



The first 100 leaves of an unbound book were turned over, 

 and a rectangular trough of the dimensions of the photographic 

 plate (7'5 by 18"°) cut into the next 55 pages. Seven pages 

 above this trough, thin metallic plates, from 5 to 20""" wide, 

 w^ere placed between two leaves and held in position by gum- 

 ming the two leaves together. Care was taken to let the 

 mucilage dry before shutting the book. After the photo- 

 graphic plate (Seed, 23) was placed in the trough, the book 

 was closed, wrapped in black tissue paper, then in paraffine 

 paper, and finally put into a tin box. 



The box was prepared as follows : Its lid was placed exter- 

 nally over its bottom and a rectangular window, 7*5 by 13*5'=™, 

 cut through them both. Thereupon a sheet of aluminium, 13 

 by 23^^°, and •29™'° thick, was placed between the lid and the 

 bottom, so as to screen the window. The wide margin of the 

 aluminium, lying between the sheets of tin, was united to them 

 above and below by thin layers of bees'-wax. Externally the 

 edges of the rectangular window were covered with sealing- 

 wax, to which a thick layer of paint was finally applied. A 

 hew lid was provided for the open side of the box and both 

 lids were soldered on. Prepared in this manner, the box could 

 be left exposed to all kinds of weather without danger that 

 moisture would reach the photographic plate. To touch the 



* This Journal, IV, vol. i, May, 1896, pp. 363, 364. 



