346 The Stmmance-Abady “Flicker”? Photometer. 
The revolving wheel has its periphery formed by two equal 
conical surfaces or other surfaces of revolution. The axes of 
the two conical surfaces are each parallel to the axis of the 
revolving wheel, at exactly equal distances therefrom, and 
the three axes lie in the same plane. The vertices of the 
conical surfaces are at equal distances on opposite sides of 
the line of sight. In manufacturing, the wheel is first made 
as a disk of uniform thickness. . It is then chucked in a lathe 
eccentrically, and a straight line motion being given to the 
cutting or grinding tool, the conical surfaces are generated. 
The wheel is then rechucked eccentrically on the opposite 
side, and the other conical surface is generated by the cutting 
or srinding tool, having the same straight line motion as 
before. The result is that the periphery of the wheel has its 
two sides uniformly sloping at equal opposite angles, while 
the ridge of intersection of the two surfaces crosses and re- 
crosses the axis of vision during each revolution. This wheel 
is driven with a motion communicated from a suitable motor, 
either spring, electric, or any form which will produce ab- 
solutely regular motion—and at the same time afford means 
for easily adjusting the speed. In the instrument shown an 
expansion governor is utilized driven at a carefully arranged 
ratio speed, but the connexion between the spindle carrying 
the governor and that carrying the reflecting wheel is not 
rigid, but effected by means of a coiled spring. The most 
perfect accuracy of centreing is essenlial. Outside the box 
are the remontoir, stopping, and starting lever, and speed — 
adjustment, a spring motor being used. 
The peculiar shape of the reflecting-wheel affords 
means for using it in manners quite impossible in any other 
form of colour photometer, that is to say, it may, at will, 
test lights at various angles from the horizontal. Having 
found the careful cutting of the angles of the wheel so vital 
it necessarily follows that when lights out of the horizontal 
are being tested, the box containing the wheel must be just 
as carefully turned on its axis for preserving the arranged 
conditions. A double quadrant scale (one scale being num- 
bered at double the actual angle) and a small sighting or 
view-finding attachment enable the angle formed by the 
horizontal of the one light and the altitude of the other 
to be accurately ascer tained, and the box to be placed at the 
correct angle of bisection. 
The photometer is made to suit any bar or scale. The 
standards of dimensions are those of the Lummer-Brodhun 
apparatus and the ordinary Bunsen disk-box. 
