110 THE MICROSCOPE. Aug 
Until within a few years the condensing lens has been 
a somewhat expensive accessory, none being for sale at a 
price less than $4 to $10. We have so often obtained 
really good results, however, by means of very cheap and 
simple arrangements that we shall describe a cheap and 
simple affair which we once made, and which seemed to 
work about as well as far more expensive articles. Any 
intelligent boy or girl can make one. 
The thing that is required first is asuitable lens. We 
found that one of the best lenses for this purpose is 
what is called by spectacle makers a cataract lens, of as 
high a power as can be had; No. 2 answers very well. 
Such lenses have a short focus, about two inches, and are 
about an inch and a halfin diameter. The cost varies 
from fifteen to twenty-five cents, according to the profits 
demanded by the dealer. 
Where a cataract lens cannot be had, very good work 
can be done with some of the cheap lenses sold for burn- 
ing glasses. In general, however, they have too long a 
focus, A good substitute for a lens is a small glass bulb 
filled with water. This we shall describe at some future 
time. 
Having procured a lens, the next thing is to mount it. 
This is easily done. Get a common letter file, such as 
can be had for ten cents, or make one by inserting an 
upright wire in a block of wood as shown in Fig, 3. 
Procure also a good bottle cork, a piece of wire about six 
inches long, and one-eight of an inch in diameter, and a 
strip of tin about three-eighths of an inch wide and six 
inches long. Bend the tin into a loop, as shown in Fig. 
1, the loop being the exact size of the Jens. The ends of 
the tin strip should be made narrow and hammered into 
a half-round form, so as to clasp the end of the wire, 
which should then be placed in the tube thus formed and 
soldered there, A little care will be required in making 
tie exact measurements, and fitting the loop so as to get 
