44 THE AMERICAN MONTHLY [March, 
Sometimes it is desired to mount prints on paper so they will not cockle 
jn drying. For this purpose a special paste is required, and a formula that 
js recommended for the purpose is as follows : 
Bee sars photographie See No. 1, 4.028: )  Wrater,.))%.) 5 5) 22 ee orere 
Glycerin, . Se eT ROZe Alcohol, \ 30) 03:40) \s) Cae Stoner 
A formula for a rapid printing paper that is said to give very good re- 
sults is as follows :—Plain white paper is floated on a saturated solution of 
corrosive sublimate in water, and then thoroughly dried. It is then sensitized 
by floating on a solution of nitrate of silver, 1 part of nitrate to 12 parts of 
water. This operation must be conducted by yellow light, and, as the paper 
is very sensitive, it must be carefully protected from daylight while drying. 
The printing is conducted in the usual manner, except that the exposure for 
an ordinary negative will only be a few (5-10) seconds in clear weather, and 
perhaps one minute at other times. The best way to make the exposure 
is to carry the printing frame out into the light covered with a black cloth, 
and expose by removing the cloth for the required time. 
The picture will ree appear very faint, and requires to be develaped: The 
developer is a solution of one part of ferrous sulphate in thirty parts of water, 
with about three ounces of glacial acetic acid. Development is carried on 
in the usual manner for dry plates, and care must be taken not to carry the 
operation too far. The picture is then washed and fixed in hyposulphite. 
The tone of such pictures is said to be of a fine neutral black, and very 
pleasing. 
Notes on diatom study. By Wm. A. Terry. 
The most convenient method I have found for the study of the motions of 
diatoms is by means of a shallow cell an inch square, made with varnish 
upon an ordinary glass slip. By filing, the cell can be made of the desired 
thinness, to be governed by the size of the objects examined and the power 
used. About the one-hundredth of an inch I have found useful. When a 
smail drop of water containing the objects is placed in this cell and the cover 
applied, a slight pressure will force out the superfluous water, which should 
be wiped off; the cover will then remain in place in any position of the slide. 
I generally cut with a knife a small channel through the varnish at one cor- 
ner of the cell for the admission of air. With this simple arrangement the 
life, motions, and habits of the diatoms, desmids, and infusoria can be easily 
studied ; by moving the slide with the fingers the objects can be kept in the 
field of view continuously. I have studied the motions of diatoms for hours 
at a time, and have watched the growth to maturity, and the multiplication 
by self-division of infusorians. By carefully adding minute quantities of 
water from time to time when needed, applied at the edge of the cover, the 
object can be kept under examination any desired length ‘of time. 
The rapidity of the motion of diatoms varies gr eatly i in different stages of 
their development, and it appears also to be varied by the temperature of the 
water from which they are taken. In the heat of summer I have found those 
taken from cooler waters to be the most active, that is, in waters exposed to 
sunlight. I have never found diatoms very plentiful in waters flowing in 
dense shade. . One striking feature of their motion is their great force; they 
are often seen pushing or “dr ageing a mass of debris of twenty times their 
bulk. I have never been able to detect any decided current caused by them 
in the water, although this is so easily seen in the infusoria in like circum- 
stances. A mass of sediment is frequently caught by them in passing and 
carried forward, passing over the diatom from rear to front in the same di- 
a} 5 eee, eel 
