648 
relatively restricted area, the menhirs, iso- 
lated standing stones, cromlechs, align- 
ments, standing stones erected in circles, 
and squares or parallels. No correspond- 
ing monuments have been found in Amer- 
ica. 
I must conclude. My time and your 
patience are about exhausted. I recognize 
my shortcomings and apologize for them ; 
but who can accomplish in one address the 
history of the first appearance of man on 
earth and, describing the discoveries of the 
century, reduce them to the limitations 
UIP LED X' 
AB asscew by eyes BA 
AT X AND X 
maces Formed 
BA by LENSES AT AB 
X AND X! 
ah & + 
woe of Ror 
and nomenclature of a new science? The 
difficulty is increased when we consider that 
the want of harmony on these subjects is as 
great among our own scientists as it is 
between them and their foreign brethren. 
THomAs WILSON. 
U.S. NATIONAL MUSEUM. 
A NEW FORM OF PSEUDOSCOPE. 
In the Wheatstone pseudoscope the left 
eye is made to see an object from the point 
of view of the right eye and vice versa, by 
SCIENCE, 
[N. 8. Vou. X. No. 253. 
means of a system of mirrors. I have re- 
cently devised a method of converting an 
ordinary stereoscope into a pseudoscope, 
which can be used to view near or distant 
objects, and which yields results far superior 
to the old form of instrument. 
If two small lenses of equal focus (5 or 6 
ems. is about right) are mounted side by 
side, they will form two inverted images in 
space lying in the same plane, of any object 
towards which they are directed. These 
images are not only inverted but have left 
and right interchanged, and when fused 
Anew Psevdoscope 
Fig — 
either by viewing them with the axes of the 
eyes parallel, or by means of a stereoscope 
will give rise to pseudoscopie vision, as will 
be readily understood by reference to the 
diagram. 
Let A and B be two points in space, B 
being in front of A. An eye at X will see 
B to the right of A, and an eye at X’ will 
see B to the left of A, and the fusion of 
these two images produces stereoscopic 
vision, B appearing nearer than A. Sup- 
pose now that XY and .’ represent the two 
