THE YOUNG SCIENTIST. 
39 
make this the circular part must be turned all 
over, and the cutting end filed down for about 
half an inch from the end. But we think the 
before-mentioned cylinder straight-fluted drills 
supersede them. In using all these drills for 
boring a hole between the centres of the lathe, it 
is a most essential thing to let the work turn 
round occasionally in the hand. A certain way 
of boring a true hole of large diameter, say | 
to 1 inch is to fix in the chuck a well-made cyl- 
inder-bit, and carefully fix the work on the sad- 
dle of a self-acting lathe, and place on the 
change-wheel used for a fine finishing cut. * * * 
For very small work the bow drill is a most 
useful tool. Bows are made in many ways, and 
from different materials. Those for sale are of 
steel, with a hook at the end, over which a thin 
catgut is looped, with another hook near the 
handle, and to alter the tension a small toothed 
wheel with a detent is used. * * The Archi- 
median drill is also used for many small pieces 
of work. This is made from pinion-wire care- 
fully twisted into the form of a very quick 
screw ; and to tap the nut for it a similar short 
piece must be made and the end tapered off to 
the bottom as if were of the thread. This done 
a hole must be drilled in the piece of metal that 
is to form the nut, and the tap, as we will call it, 
be driven through it. This will form a corres- 
ponding screw for the long one to work in, 
* * * To know how such a thread is put into 
a piece of metal may be of service for other pur- 
poses. — Forge and Lathe. 
PolisMng and Fmishing Metals. 
We now come to the means adopted for fin- 
ishing and polishing steel and iron. Take, for 
instance, a surface of steel as an example— the 
square stem of a drilling instrument will form 
a very good subject. After it is roughed out, 
and the work all done, it must be draw-fi led, and 
this must be done with a superfine Lancashire 
file, and the lines must be kept quite straight, 
otherwise it will require so much emery-paper 
that the edges will lose the sharp angles which 
are the beauty of the work. Any ordinary 
workman can rub away with emery-paper, but 
in so doing he may spoil the appearance of a 
piece of good work, and that without knowing 
it. To avoid this, the smoother and better it is 
filed the less paper will it require. To get the 
beautiful finish we see on the best work, a piece 
of flour emery-paper, well worn, and a little oil 
upon it, will be found the best thing to use, and 
when this has been well worked, to get the high 
polish, a piece of wood flat upon the surface, 
with some fine crocus, will bring it up to this 
state ; and if any deep scratches be there, you 
will at once observe them, and to remove them, 
in all probability, it will have to be filed all over 
again. Now, to avoid all this loss of time, great 
care must be taken that the scratches are re- 
moved before any attempt is made to polish. 
Having finished the work so far, many prefer 
to see it left straight; others, again, like to see 
it in some way ornamented. Now, there are 
several ways of doing this. First, then to cross 
the surface. This is done by folding a piece of 
emery-paper tightly round a file, but the pro- 
cess is not the merely pushing it across the 
work and making a mark, but it requires some 
practice to produce a good pattern, and the 
wrist must take a kind of circular action, and by 
doing this each line becomes, so to speak, con- 
nected, and makes a much better finish than a 
series of lines only. Another process of flnishing 
steel is to curl all over the surface with a piece 
of oil-stone that will cut. This is a most difficult 
thing to obtain, as very few stones will cut steel 
to leave the bright marks necessary to give it 
the appearance desired. When a piece of this is 
once obtained it is really a prize, and if it wears 
away it may be inserted as far as possible into 
a wooden handle. To use the stone when it is 
once obtained is the next thing. This is done 
by holding it firmly in the hand and moving it 
about in all directions, like curling brass. There 
is no stated number or size of the curl, but this 
is quite a matter of taste, and must be left to the 
operator. Another way of finishing iron and 
steel is with the scraper, which is used with 
both hands, and the work must be scraped in 
various directions, but with regularity. Large 
surfaces are sometimes done in this way. Lathe- 
beds are at times done so, but we think this is 
somewhat out of character, as the fact of con- 
tinually drawing the poppit-head up and down 
the bed produces a series of lines which look 
most unsightly. Regarding all this, it is all a 
matter of taste, and the style of finish ^must be 
left to the operator.— jFbrgre and Lathe. 
Rat Pie.— The Eev. J. G. Wood, the well-known 
English naturalist, in a lecture the other day said 
that there was literally nothing of which he (the 
lecturer) was so fond as a rat pie. This was a dish 
which frequently made its appearance on his 
table, and was enjoyed by all his family. He had 
several friends, too, who, as he had, had overcome 
their prejudice, and thoroughly enjoyed a good 
helping of rat pie. 
Paste for [Mounting- Photographs.— Mix 
throughly 630 grains of the finest Bermuda ar- 
rowroot with 375 grains of cold water in a capsule, 
with a spoon or brush ; then add 10% ounces of 
water and 60 grains of gelatin in fine shreds. 
