AMERICAN 
JOURNAL OF SCIENCE AND ARTS. 
[SECOND SERIES.] 
Art. XVIL—On the Phantascope ; by Prof. J. Locxe. (Ina_ 
Letter to the Editors. ) 
As many persons find it difficult if not impossible to converge 
the optical axes, (or in common phrase to look “cross-eyed,”) for 
the purpose of making the experiments lately described by me, 
under the head of “ binocular vision,” I have invented an instru- 
ment which enables all persons to succeed in obtaining the chief 
results. It is very simple, having neither lenses, prisms nor reflec- 
tors, the object being in general the same as holding the finger or 
other object near the eyes and concentrating the attention upon 
it for the purpose of optical convergence. 
It consists of a flat base-board about nine by eleven inches, 
With an upright rod at one end bearing two sliding sockets to be 
clamped at any elevation like those of a retort stand, or adjusta- 
ble by stiff sliding springs. ‘The upper socket supports horizon- 
tally a small vane or card, having a slit or sight hole one fourth 
{ an inch wide and three inches long from right to left. This 
slit has its middle directly over the center of t rd, and 
18 intended to have the eyes directly over it, one eye at one end 
and the other at the other ;—two small holes, say one fourth of an 
ch, occupying the place of the ends of this slit would answer, 
except for the unequal distances between the eyes of different ob- 
Servers. The lower of the two sockets bears horizontally a mova- 
ble screen of pasteboard or thin wood, having a slit at least three 
inches wide Ms left to right, and about one inch in the other 
Stconn Serres, Vol. IX, No. 26.—March, 1850. 20 
