March 27, 1896.] 



SCIENCE. 



467 



The difficulty found by Professor Emer- 

 son and myself in precisely rejjeating most 

 of these experiments has doubtless been ex- 

 perienced by others working with the 

 X-rays. When the conditions of an ex- 

 posure seem identical with those of a pre- 

 vious one, the results often differ, from vary- 

 ing excitation of the tube, or possibly slight 

 shifting of the source of the rays, or from 

 numerous other causes difficult to control, 

 A confirmation of results by other observers 

 is therefore valuable.* 



Since the last paragraph was in type I 

 have succeeded in proving that the ' fringe ' 

 is due to the spring by the somewhat sur- 

 reptitious method of placing a second 

 ■Crookes tube behind the plate, and thus 

 projecting a shadow of the spring itself 

 upon the plate on which at the same time 

 the spring was reflecting the fringe. Fig. 

 2, is from a plate obtained a fortnight 



Fig. 2. Showing Reflection and Intee- 

 fe.bence of x-rays. 



* In a previous communication ( p. 235) , a slip of 

 the pen made me invert the order of permeability of 

 hard rubber, glass and brass ; the rubber is of course 

 the most permeable. 



ago. A silver dollar lay on the slide 

 above the plate, directly over the spring 

 which was behind the plate ; the tube was 

 14 mm. above the plate and the exposure 

 was one hour. The X-rays must have 

 passed through the silver dollar and then 

 have been reflected by the spring, giving 

 the ' fringe.' Since the central bright line 

 is much brighter than the other portions of 

 the plate partially screened by the dollar, 

 it would seem that this additional bright- 

 ness can only result from the superposition 

 of waves in the same phase, or, in other 

 words, from something closely akin to inter- 

 ference. Similar fringes have been obtained 

 through tinfoil instead of silver, and also 

 where no obstacle intervened between tube 

 and fllm. We hope by this method to ob- 

 tian the wave-length of the X-rays. 



Edwin B. Frost. 

 Hanovee, N. H., March 10, 1896. 



THE RECEPTION OF FOREIGN STUDENTS IN 

 FRENCH UNIVERSITIES AND SCHOOLS. 

 In order to carry out effectively the plan 

 for the reception of foreign students in the 

 schools of France, in which there is now 

 so much interest, the French government 

 has formed a Committee of Patronage for 

 the purpose of receiving new comers, giving 

 them encouragement, and furnishing them 

 with all necessary information in regards to 

 their studies and facilities for life in the 

 university towns. The object of these 

 Committees is to make the student's stay 

 in France agreeable as well as profitable. 

 They also offer their friendly offices to the 

 families of students. 



THE PARIS COMMITTEE. 



The Paris Committee has its headquarters 

 at the Sorbonne, and is composed of the 

 following members : 



MM. Emile Boutmy, Member of the Institute ; 

 Director of the Eeole libre des sciences politiques 

 Michel Br^al, Member of the Institute. Xavier 



