362 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
The result of the following comparison between the new Zeiss field- 
glass of 6 power and an old Galilean binocular of 7 power shows that 
the Zeiss had the better definition, and the Galilean the more light. 
Power 
Weight. 
Length 
Diameter of held 
Diameter of objective 
Focus of objective 
New Zeiss. Old Binoculars. 
6 7 
12 £ oz. 14^ oz. 
in. in. 
6° full 2° bare 
6/10 in. 2i in. 
4| in. 9 in. 
The new instruments are made of three powers, 4, 6, and 8, and the 
author considers that for field, tourist, and ordinary purposes they have 
no rival. 
The stereo-telescopes are constructed on the same principle as the 
field-glasses, but in them the ray is not bent back on itself. They may 
be used in two ways. In the first position the bodies of the telescopes 
point to the right hand and left hand of the object which is to be observed 
(fig. 55), while the axes of the eye-pieces are directed towards it. The 
greatest stereoscopic effect is thus obtained, while the object can be 
observed from behind cover, such as a tree or post. In the second 
position the bodies of the telescopes point up to the zenith. Here there 
is less stereoscopic effect, but it is possible to look over a wall without 
being exposed. These instruments also are made of three powers, viz. 
6, 8, and 10. 
In these new instruments each eye-piece screws in and out by itself, 
so that each eye can be focused for itself. 
Fig. 57 is a plan showing the prisms in their proper positions as 
looked at from the object-glass. The larger circle represents the object- 
glass, and the smaller the field-lens of the Huyghenian eye-piece. The 
letter R, drawn on the object-glass, is made to represent the rays from 
an erect image falling on the object-glass. When the raj?s are brought 
to a focus by the object-glass, the erect image will be inverted and trans- 
posed. But because of the action of the upper prism in fig. 54, the 
inversion is corrected, while the transposition is left. The second 
prism, i. e. the lower one in fig. 54, whose edge is at right angles to 
the first prism, corrects the transposition, while the corrected inversion 
remains unaltered. 
Klein’s Lens with Micrometer.* — Herr F. Becke describes an 
arrangement for measuring the small interference figure which is 
obtained with the Czapski eye-piece by inserting an iris-diaphragm in 
the plane of the image. The author does not remove the Ramsden eye- 
piece and examine the image formed directly by the objective, but with 
an aplanatic lens — the Klein’s lens — observes the image which is formed 
above the Ramsden eye-piece. 
The apparatus consists of a cylindrical tube-support which slides 
with slight friction over the head of the Czapski eye-piece. In the 
upper part of the support is an adjustable aplanatic lens with magnifi- 
cation of 8 times, and an eye-piece micrometer (10 mm. divided into 
100 parts) which can be adjusted by two projecting pins. 
* Tscherraak’s Mineral, u. Petrogr. Mittheil., xiv. (1894) pp. 375-8. See Zeitaclir, 
f. wiss. Mikr., xi. (1895) pp. 500-1. 
