ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
101 
two objective lenses must be exactly alike ; not only of the same shape, 
but also alike in magnifying power and in point of clearness. (The same 
care must be taken, whether the lenses be concave or convex.) Again, the 
telescopes must have the same “ ordinate,” so that not only the objective 
lines, but also the eyes similarly placed will correspond precisely to 
each other ; but the telescopes and their first ocular lenses must be as 
far apart as is the distance between the centres of the pupils of the two 
eyes. The telescopes should be so directed toward one and the same 
object as if there were but one aperture for both tubes, and through this 
aperture the object, brought wonderfully near, can be very distinctly seen. 
‘ VI. Since there are various kinds of telescopes, the ordinary Galilean, 
made of convexo-concave lenses, others convexo-convex, which can bo 
made from pure convex lenses, and, indeed, again, out of these others 
can be so formed that they present objects inverted, as it is said to be 
the case with astronomical telescopes. Others present the object erect, 
but whether straight or curving inwards depends on the nature of the 
ordinate. The former can be made from four convex lenses, the latter 
from a plane glass and two very powerful lenses, &c. Thus also various 
binocular tubes can be made, depending on the ordinates of the telescope, 
provided that the ordinates be the same for the same binocular tube, 
taking the distance of the first ocular lens and the direction of both 
ordinates through one aperture, so to speak, so that the same object will 
be seen single and not double. 
‘ VII. For lesser binocular tubes common telescopes not exceeding a 
foot in length are best, because those more than a foot long do not present 
the object completely enough. The smaller the telescopes the greater 
the object. Tubes of this kind are made with three lenses for each tele- 
scope, having their ordinates placed as indicated in No. 13, cap. 5, seq. 
The proportion of the lines there indicated is also much approved. 
‘ VIII. How to join the two telescopes. The two tubes may be made 
of copper or brass plates, as in fig. III., where two tubes A and B are 
joined by brass hinges at a b c ; then, where the tubes are placed, both 
eyes are accommodated to any remote object, and the object will appear 
single and with great clearness. How the tubes may be joined, placed, 
closed, and covered is shown in fig. IV. Likewise several movable rods 
similarly connected could be placed in each tube, but this method has 
disadvantages. Two tubes with their lenses arranged so as to bo adapted 
to any vision are best constructed by cases or capsules as follows: — 
Make a capsule of brass leaf in the form of an ellipse, as shown in H 
(fig. VI.). Make two apertures in the lesser capsules E and F as far 
apart as the distance between the eyes. These apertures must also be 
elliptical, as E and F in the figure. The size of the apertures should 
be such that the tubes or rods A and B, also C and D, would perfectly 
correspond. 
‘ The two discs E and F of both tubes must be so firmly fastened that 
the tubes will not slide up and down too easily. Thus we now have all 
things arranged as in the figure G. This entire affair can be put into 
the greater capsule II and there encased. Thus it can be easily and 
safely carried about. The capsule H may be of wood, leather, or other 
material, and decorated to suit the taste. 
‘ IX. Since the distance between the two eyes does not differ much 
