760 



SCIENCE. 



[N. S. Vol. V. No. 124. 



the rays the refracting body has been in 

 the form of a prism. This involves the in- 

 convenience that the absorption of the rays 

 is so much greater toward the thicker por- 

 tion of the prism as to cause imperfect or 

 unequal definition in the image of the slit or 

 wire used for the test. This has sometimes 

 given rise to the appearance of a deflection 

 of the rays awaj' from the base of the prism 

 instead of towards it, a negative action, 

 implying a refractive index less than 

 unity. 



In the present experiments this was 

 avoided by employing for the refracting 

 bodies thick pieces of glass and Iceland 

 spar with parallel sides, which were in- 

 clined at an angle of 45° to the path of the 

 rays. The distances traversed by the rays 

 in the two media were about 10 and 14 mm. 

 respectivelj'. The displacement of the image 

 for ordinary light is about 1.5 mm. for the 

 glass, and for the Iceland spar about 1.0 

 mm. and 1.8 mm. respectively, for the two 

 images due to double refraction. A small 

 platinum wire, stretched so as to be quite 

 straight, rested upon the upper surfaces of 

 the plates, and the rays from the tube were 

 passed through a narrow slit in a copper 

 plate. The slit was parallel with the wire 

 and at a considerable distance from it. A 

 strong and very clearly defined image of 

 the wire was formed upon the photographic 

 plate, showing no displacement by the glass 

 plate or the Iceland spar, and no trace of 

 widening or duplication by the latter, or, in 

 other words, no perceptible effect of refrac- 

 tion, or double refraction. 



Other experiments were described, in 

 which very sharply defined images of fine 

 platinum wires produced by the rays 

 upon a photographic plate showed a faint 

 central band, dark in the negative but light 

 in the positive, corresponding to the familiar 

 bright central band behind an opaque wire 

 in the case of luminous rays. The con- 

 verse effect of a dark central band in the 



positive from a narrow slit was also ob- 

 served, but less distinctly. These results 

 oflfer some support to the idea of ti-ue diffrac- 

 tion and the periodic character of the rays, 

 but the matter must be regarded as some- 

 what uncertain until secondary maxima 

 and mimima are obtained, which would 

 settle the question of diffraction and per- 

 mit the definite determination of wave- 

 lengths. 



A3IEEI0AN ASSOOIA TION FOR THE ADVANCE- 

 MENT OF SCIENCE. 



A MEETING of the Council of the American 

 Association for the Advancement of Science 

 was held at "Washington, D. C, on April 

 1 2th. Owing to the lamented death of Pro- 

 fessor Edward D. Cope, the late President 

 of the Association, Professor Theodore Gill 

 presided as Senior Vice-President. A num- 

 ber of members wei-e elected, and several 

 matters of importance relating to the De- 

 troit meeting were discussed and arranged 

 at this meeting. 



Professor Leland O. Howard, of the De- 

 partment of Agriculture, Washington, D. C, 

 was nominated as Vice-President and Chair- 

 man of Section F,to fill the vacancy caused 

 by the death of Professor G. Brown Goode. 

 Professor Howard was requested to prepare 

 an address to be delivered before the Section 

 at the Detroit meeting. 



Professor I. C. White, Vice-President and 

 Chairman of Section E, will go to St. Peters- 

 burg this summer as one of the delegates to 

 the International Congress of Geologists. 

 He will, however, prepare his Vice-Presi- 

 dential address to be read before the Section 

 at the Detroit meeting. 



On Monday evening, August 9th, at the 

 Detroit meeting. Professor Theodore GiU 

 will deliver a memorial address on the life 

 and work of Professor Cope, at the time and 

 place appointed for the Presidential address, 

 which was to have been given by Professor 

 Cope. In this address Professor Gill will 



