DEFINITE EKtURES BY THPI DEPOSTITON OF DUST. 
19't 
4 mlllims. from the edge of the plate at both ends, and is conical in form. If the 
strip had been of the same length as the plate, the deposit would liave reached, as 
shown in former experiments, very nearly the whole length of the plate. If the 
hanging screen 1)e raised 2 millims. above tlie plate, then in place of a long line of 
deposit there is a line of clear space some 7 mlllims. wide, and at the ends are delicate 
curved lines extending to the corners of tlie plate, and beyond this open space there 
is the conical deposit as in tlie former case (fig. 39). In raising the screen so that it 
was 4 millims. aliove tlie plate, the depth of the clear space increased and Was now 
12 millims. from the edge. When the screen was 6 millims. above the plate, the 
clear space became strongly curved, and at the top of the curve was 20 millims. from 
the edge of the plate, and when 10 millims. above the plate the normal rays of the 
cross were well developed, and a well defined but slightly distorted cross was formed. 
