154 On the Phantascope. 
direction, with its center also perpendicular over the center of the 
base-board. ‘This screen has marked vertically across its middle 
an index, shown by two arrows in the figures marked I. 
E 
eas 
I 
bi 
2 
a | e ’ 
SS i rd 
UL. 
| 
E. Eye screen—I. Index screen—B. Base-board. 
Evxperiments.—In experimenting with the Phantascope, the 
operator places whatever is to be tried upon the lower tabular base- 
board, looks downward through the upper slit and slides the 
screen up or down until he attains the adjustment required. 
