INTENSITY OF CORONAL LIGHT DURING THE SOLAR ECLIPSE OF 1886. 367 
made, become invisible at the same time. The majority of screens fulfilled this con¬ 
dition, and the best as regards uniformity of,size of spot and freedom from grain in 
the paper were selected for use. The screen, as will be seen from the figure, was 
mounted in a circular frame, which could be rotated so as to bring the sjDots into any 
desired angular position. It could be removed at pleasure by releasing it from the 
buttons which held it in position. 
Fig. 1. 
To hold the screen a box was constructed, as shown in fig. 2. It was made as light 
as possible, panels of card (as at P, P) being used instead of wood when practicable. 
The glow lamp to be employed was fixed in a holder inside the box; this could move 
along the slot A, and lie fixed by a thumbscrew, H, in any desired position. (It may 
here be remarked that the plane of the filament was at right angles to the axis of the 
tube.) 
At the end B was an aperture into which the sliding tube of the telescope fitted ; 
at D was a door, which could be opened to adjust the lamp. The screen shown in 
fig. 1 was inserted at S, and held in position by means of buttons. At 0 was an 
opening, which was covered by a black velvet bag into which the head of the observer 
