THE YOUNG 
and easily one may acquire proficiency in 
the art. 
Precious stones are cut in the same way, 
except an iron wheel is used instead of a 
copper one, and diamond dust instead of 
flour of emery. 
Fern Pictures. 
A SIMPLE photographic method of 
making fern pictures is thus de- 
scribed by the Chemist and Druggist: 
Cover a sheet of paper with a weak solu- 
tion of salt in water and some white of an 
egg, well beaten ; after it is dry, take it 
Into a dark room, and with a tuft of cotton 
pass over it a solution of nitrate of silver 
<50 grains to an ounce of water) ; dry it in 
the dark, and the coat of chloride of silver 
formed on its surface will receive the im- 
pression. Then arrange your ferns be- 
tween two plates of glass, and cut the 
paper to the same size as the glass plates ; 
place it under them and expose to the 
sun, in the same way as a photographer 
prints a portrait. Watch it until dark 
enough, and before removing the paper 
from the glass take it into a dark room. 
Here place the picture in a solution of 
hyposulphite of soda, which will dissolve 
the chloride of silver, but leave the de- 
composed material (finely divided black 
silver) which forms the black background, 
while the shadow of the leaves will be 
white. 
The old method of spm?/ or spatter work 
also gives very good results : Take a sheet 
of strong white paper, and with an atom- 
izer pass over it a spray of very diluted 
mucilage, so as to obtain a very thin and 
slightly sticking film, which will make the 
ferns adhere of which it is desired to make 
the picture. The ferns and leaves must 
have been first pressed in a book, and 
•after arranging them to suit your taste, 
cause them to lie as closely to the paper 
as possible; fill an atomizer with very 
diluted India ink, and blow a spray over 
the ferns, more or less in proportion as 
you want a darker or lighter shade. It is 
well to do this with intermissions, letting 
it dry a little, so as to avoid excess of 
moisture and possibility of running the 
liquid into drops. When nearly dry, but 
SCIENTIST. 81 
still a little moist, remove the ferns, which 
may be used over again several times, each 
time being arranged in different figures. 
Instead of causing them to stick with 
mucilage, however, it is best to fasten the 
ferns to the paper lightly with fine pins. 
The figure of the fern is left white on a 
grey ground, and the figure of the fern 
leaves may be greatly improved by vein- 
ing them with a pencil. 
For an atomizer use either the old plan 
of a brush drawn across a sharp edge, or 
over a piece of wire netting, such as a coal 
sieve, or use the method described in a 
fomer number of this journal. 
Home-Made Telescopes and Micro- 
scopes— VII. 
ON THE PKODUCTION OF SPHERICAL SURFACES 
IN GLASS. 
HAYING got our lens perfectly smoothed 
and figured, the next operation is the 
polishing. It is almost impracticable to 
perform this in the hard mould, and 
therefore various substances are em- 
ployed of a less degree of hardness, in 
which the coarser particles of polishing 
powder may become imbedded. 1. For 
the larger sized lenses in microscope 
work, beeswax, hardened with some resin 
and finely- washed ochre, is very suitable, 
but for medium sizes this is too soft and 
yielding. 2. A mixture of shellac and 
washed putty-powder is therefore em- 
ployed, which is very enduring. These 
are melted together and stirred diligently ; 
the shellac is added until the whole ar- 
rives at the consistence of thick paste; 
and as the lac is apt to burn, to prevent 
this a lump of beeswax should be thrown 
into the mass. This does not actually 
mix with the other ingredients, but lessens 
the risk of spoiling the composition by 
overheating ; when cool enough the mass 
may be rolled into sticks between two 
greased boards. 
For the very smallest lenses, such as the 
fronts of a l-25th and a l-50th, the last 
composition is still too soft and fragile to 
maintain a true figure. The polishing 
I mould is therefore, for these, made in the 
[ end of a rod of pure tin, which is cut out 
