236 A. W. Wright — Cathode Rays and their Effects. 



tion nor polarization, that they do not produce perceptible 

 heating effects, nor influence the magnetic needle. These 

 characteristics differentiate them strongly from luminous rays, 

 and he suggests, but with great moderation in statement, that 

 they may be longitudinal waves in the ether. To these ques- 

 tions of high scientific importance, were added descriptions of 

 results obtained in the production of photographic pictures of 

 objects through considerable masses of matter opaque to light, 

 thus revealing the inner structure of bodies otherwise invisible, 

 and even showing, in the body of an animal, the bones clearly 

 distinguished from the flesh. 



These results were of such great interest that physicists were 

 immediately incited to test their reality, and to witness the 

 novel effects. The present paper gives an account of experi- 

 ments made by the writer in the Sloane Physical Laboratory 

 of Yale University, and, omitting many details, follows the 

 general course of the work as it was carried out. 



For the production of the cathode rays, a Crookes' tube, 

 nearly spherical in shape, was used, of the kind often employed 

 to exhibit the independence of the negative electrode in high 

 vacua. It is provided with four electrodes, three of straight 

 wire, of which two are situated at the opposite extremities of 

 a diameter and directed radially, while the third is placed at 

 the end of a diameter at right angles to the line of the other 

 two. The fourth is situated a little to one side of the point 

 opposite the third electrode just described. This disposition 

 is advantageous, as it leaves a space of smooth thin glass 

 opposite the third and fourth electrodes, which were the ones 

 employed, sometimes one, sometimes the other, as the cathode. 

 The fourth wire terminates in a slightly concave disk or 

 cup about two centimeters in diameter. The concave disk 

 concentrates the cathode rays, issuing normally from its sur- 

 face, at a point near the opposite surface of the tube, send- 

 ing them through a small area of the glass wall, which becomes 

 strongly heated. The photographic plates show this concen- 

 tration of the rays plainly. On account of the unequal distri- 

 bution of the effect, however, as well as because of the inferior 

 definition of the pictures thus obtained, the third straight wire 

 electrode was used in preference. This gave somewhat less 

 intense effects, making a longer exposure necessary, but the 

 results were otherwise much more satisfactory. The induction 

 coil used with the tube gives a spark of six or seven centi- 

 meters in air, and was actuated by four, sometimes five, second- 

 ary cells. 



The first photograph obtained with this apparatus, on Jan. 

 27, was made upon a piece of bromide paper which had been 

 wrapped in thick black paper. It gave very clear representa- 

 tions of the objects employed. In the evening of the same 



