102 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
for many individuals, and also since the eyes easily accommodate 
themselves, many artificers fit their own eyes and fasten the rods in the 
tubes firmly in one position, so that they cannot be moved. I have 
made many such myself. Although they fit most people well enough, 
yet some eyes are unpleasantly affected after looking steadily for a long 
time. Least of all mu-t such tubes be used for magnifying, unless 
they be adjusted to the distance between the eyes, since they harm the 
eyes not a little, and when used too much may even turn the eyes from 
their natural position (cross-eyed), as I have known happened to a 
certain nobleman. Thus it is always better to make the rods movable, 
so that they can be fitted to all eyes ; yet it is allowable to make a little 
common binocular tube with movable rods, to be placed in a case after 
the manner of a little book, thus : Make a small capsule the size of the 
tubes which it is to contain, cover this with leather, and put on clasps 
just like a little book. Put two thin wooden tablets at the ends where 
the ocular bands and objectives meet, but where the clasps are opened. 
These must be shoved aside, so that the eyes can look through the tubes. 
The cases may be so constructed that the open space between the two 
tubrs can hold the “ ignitabulum” with its sulphur thread (match-box) 
aud the burning-glass for quickly making a fire in the field or anywhere 
you please. Above this space a cover of thin brass is placed, on which 
is fixed a magnetic needle. At the other end, which is covered with 
leather where the book closes, can be placed a movable circle to point 
to the moon, according to the hour of the night ; and thus various other 
things can be added. 
‘ X. The long rods holding the lenses can be of various materials and 
shapes, but it is best to be so made that the lenses can be cleaned when 
necessary, for they will become dusty, no matter how carefully they are 
closed. That part of the tubes just before and just behind each ocular 
or objective lens should be so arranged that a small linen cloth could 
be inserted through an aperture for the purpose of wiping the lens. 
‘ XI. In convexo-convex binocular tubes it is better for the first ocular 
lenses to be quite acute, so that the eyes can be placed nearer the same 
objects. They should always be a little more acute at the bottom than 
in simple convexo-convex tubes, since there is a greater clearness from 
the two eyes looking at the same thing. I have found these to be good 
proportions : — The objective lenses remove the focus to a distance of 
IE ft. ; the middle ocular lens, equally convex on each side, has a dia- 
meter 35/100 Korn. ft. ; the first ocular lenses anywhere from a diameter 
20, 100. This is also a good binocular tube. Objective lenses remove 
the focus to a distance of 2 ft.; middle lenses, equally convex, 40/100 
diameter; first lenses, near the eye, 20/100 and 25/100 diameter. 
Another good tube, objective lenses at a focus of 4 ft. Middle lenses, 
equally convex on all sides, 50/100 diameter. First ocular lenses, 
unequally convex, from diameter 30/100 and 35/100. 
‘ XII. Two convexo-convex telescopes inclosed in a case can be made 
adjustable to any vision in the following manner Join the two tele- 
scopes by movable arms (as indicated in No. 8 of this chapter), and 
through these arms place a spiral screw, which can lengthen or shorten 
the telescope at will. This is shown in the 7th figure. ABC is a nail 
cylindrically round from A to B, spirally round from B to C. At B is 
a small nail, by which the large nail A B C is kept in place after being 
