On the Reflection of Cathode Rays. :381 



fluorescence on the glass beyond, throwing upon the latter a well- 

 defined shadow of the vanes of the mill wheel. Under these conditions 

 the wheel was found to rotate, but not in the direction anticipated ; in 

 fact, for either position of the anticathode the direction of rotation 

 was most persistently opposite to what would be expected on the 

 supposition that the driving force was the impact of the reflected rays. 

 When the position of the anticathode was suddenly moved so as to 

 reflect the rays first through one aperture and then through the other, 

 the direction of rotation immediately reversed itself, the direction of 

 rotation being always as though there was some attractive force between 

 the anticathode and the particular vanes upon which the reflected rays 

 were at the moment falling. 



These and further experiments, made with another arrangement in 

 which instead of a single bulb divided by a mica diaphragm, two sepa- 

 rate bulbs were used, one containing the cathode and anticathode and 

 the other the mill wheel, united by a pair of glass tubes corresponding 

 to the apertures in the mica, appear to show that whatever may be 

 the cause of the inverse rotation of mill wheels which are not directly 

 acted upon by cathode rays, this is not due to the direct mechanical 

 force exerted by the impact of reflected cathode rays, but to some 

 other force or forces of a much more potent nature. 



Tlw Mode of Reflection of Cathode Rays. 



The reflection of cathode rays is largely diffuse, but does not appear 

 to be altogether so, as the writer has already pointed out,* and since 

 more completely verified by the following further investigations. 



In the first place, experiments were made to see whether any direct 

 visual evidence of specular reflection of cathode rays could be obtained 

 with a spherically concave reflector. For this purpose the tube shown 

 in fig. 4 was constructed. In this tube the cathode C is made of alu- 

 minium 1-25 inches diameter, and is spherically concave on its active 

 surface with a curvature of a 10-inch sphere, so as to give a fairly 

 parallel beam of cathode rays. The anti-cathode A consists of a cir- 

 cular disc of platinum about 0*9 inch diameter, stamped into a mould 

 having a curvature equal to that of a 10-inch sphere, the concave sur- 

 face of the platinum being highly polished. The anti-cathode is 

 mounted on a vertical spindle, arranged in guides, and furnished with 

 a small brass bob weight attached to a horizontal arm, so that by 

 tapping the tube the anti-cathode can be rotated round its vertical axis 

 into any desired position. The diameter of the spherical bulb, at the 

 centre of which the anti-cathode is placed, is 3*6 inches, and an addi- 

 tional wire electrode is provided in an annex at the top to serve as 

 anode. In experimenting with this tube, a 10-inch induction coil, with 

 * ' Roy. Soc. Proc.,' TO!. 63, p. 436. 



