On Photometric Paddle-Wheels. 
683 
1910 - 11 .] 
while running, and possessed of the great advantage of having its rotating 
part in one piece only. 
A mathematical discussion of this new type of apparatus follows, in 
which are deduced formulae for the intensities of the light transmitted 
under different conditions, and for the greatest width of the beam of light 
that can be employed ; and a graphical tabulation of the values of these 
formulae in different cases is provided. 
The mounting and details of an actual instrument are described ; 
together with an additional mechanism for the purpose of automatically 
recording the photometric measurements obtained. 
{Issued separately October 24 , 1911 .) 
