THE YOUNG SCIENTIST. 
89 
wiping must be as gentle as possible; 
rubbing is inadmissable in any case. 
Proctor advises sweeping from a small 
space near the edge as a centre. Any 
refractory stains may be breathed upon, 
or touched with pure alcohol, and wiped 
till dry ; but if the glass has become dis- 
colored, we must put up with the defect ; 
and care should be taken not to mistake 
specks in the substance of the glass for 
foreign matters lodged on its surface. A 
slight tarnish may frequently be removed 
from a metallic speculum by lemon-juice, 
or a solution of citric acid, or spirit of 
hartshorn, carefully wiped off in a short 
time ; if this does not restore its bright- 
ness, it is better to leave it alone ; a slight 
loss of light is not so great an injury as 
would result from strong friction. The 
taking out or replacing of an object-glass 
or mirror is a delicate operation, and 
hurry or carelessness may easily make it 
a very dangerous one ; speculum metal is 
nearly as brittle as glass : but this ma- 
terial is rapidly going out of use, from the 
superiority of the silver-on-glass mirrors, 
which are now becoming appreciated as 
they deserve. The management of these 
need not be described here, as special 
instructions should always accompany 
them, such as will be found in Brewing's 
" Plea for Keflectors," or Calver's " Hints 
for Eeflecting Telescopes." 
Dimness of vision often results from 
damp on the eye-lens. This will rapidly 
disappear, without wiping, in a warmer 
temperature. If the finder does not act 
well, this may be suspected to be the 
cause. For these and many other rea- 
sons, a small lamp, the light of which 
can be concealed at pleasure, is a con- 
venient adjunct to the telescope; any 
glass surface held at a safe height over it 
will speedily be cleared of moisture. A 
ground or papered glass front to a lamp 
is advantageous for reading. 
Eye-piece lenses require occasional 
wiping; the leather may be pressed to 
their edges with a bit of soft wood. A 
piece of blotting-paper rolled to a point, 
and aided by breathing, answers perfectly. 
Their flat faces are easily scratched if 
laid downwards on a table. The screws 
demand very gentle usage: a previous 
turn backwards, before screwing in, 
causes the thread to fall with a snap into 
its place. ^ ^ ^ 
Hand-Turning. 
I NEED scarcely insist on the actual ne- 
cessity of everyone learning, first of 
all, to turn by hand. I have found the 
want of knowledge of the first rudiments 
of turning very much against the progress 
of anyone desirious of becoming an ef- 
ficient. I know very many amateurs who 
can ornament a box well enough, for 
example— equal, in fact, to anyone who 
does such things professionally; but if 
they had to turn the box for themselves, 
it is certain it would not be ornamented 
at all. Therefore it is an absolute neces- 
sity for learners to begin at the begin- 
ning, and progress gradually to the 
various grades. Authors generally begin 
with soft-wood turning, and represent it 
as the most easy to accomplish. That it 
should be the first thing commenced on, 
I grant; but that it is the more easily 
acquired I do not admit. This, however, 
is a matter of opinion, and needs no dis- 
cussion here ; so to the point. In begin- 
ning, as a tyro, all that will be necessary 
is a plain lathe, the size or height of 
centre of which is of no consequence— but 
I should advise a 5 inch centre lathe— and 
the tools required will be simply a gouge, 
chisel, a:nd parting-tool. The latter most 
people who essay to write upon this sub- 
ject seem to ignore. I admit that a good 
deal of work can be detached with the 
edge of the chisel, but still the parting- 
tool is a necessary adjunct, and will be 
wanted. The wood I should recommend 
will be any soft wood, such as pine, ma- 
hogany, tulip, king, and many others of 
this class. Having arranged the tools 
and selected the materials, we will begin 
by placing upon the lathe the prong- 
chuck, which is made of metal, with a 
steel prong screwed into it. This part is 
made with a centre, and the fiats filed 
down to the size of the largest end of the 
point, each side being then filed like a 
wedge, the bevel being, of course, to the 
rear. This, it will be obvious, will not 
allow of the two face-lines being diame- 
trically opposite, as would be the case if 
