THE YOUNG SCIENTIST. 
43 
sents this block cut through the middle 
of the hole, to show how it is bored. Lay 
this block upside down upon some smooth 
surface, either wood or metal, preferably 
the latter. Now melt some block tin or 
tinsmith's solder on a ladle, and pour it 
into the mould thus placed, taking care to i 
hold the block in place while pouring. 
Fig. 4. 
On removing the cast metal from the 
mould, it will present the appearance of a 
bolt with a circular head and without a 
screw thread. Centre this as exactly as 
possible in your lathe, putting the spur 
centre into the smaller end, and turn the 
smaller part into a spindle like that of the 
spur centre, so that when the spur centre 
is removed the tin spindle will fit into the 
mandrel smoothly and tightly in its place. 
Have it go in far enough so that the tin 
head will rest firmly against the end of 
the mandrel. A few trials during the pro- 
cess of turning will enable this to be done 
with sufficient exactness. If this has 
been properly done, on revolving the 
mandrel the end of the tin which projects 
Fig. 5. 
from it will be free from noticeable " wab- 
bling" motion. Then set the slide rest 
of the lathe squarely in front of the tin, 
rest the convex gouge upon it, place the 
cutting edge against the middle, which is 
marked by the tail-stock centre, set the 
lathe in motion and turn the metal out 
until you have a smooth concavity in the 
end of the tin a little larger in diameter 
than the proposed lens ; then dip a piece 
of slightly moistened flannel cloth into 
"putty powder," and polish this con- 
cavity, being careful not to polish it out of 
shape. This concave surface must be so 
true that when the convex gouge used as 
a gauge, is placed squarely against it, no 
light can be seen passing under it. Fig. 5 
represents this tin polisher when finished. 
The last preliminary to the grinding of 
the glass is to turn a piece of hard wood 
into the shape of Fig. 5, except that the 
end must be plane instead of concave, and 
the head should be turned down to the 
diameter you propose to give the lens. 
To be continued. 
miUvml §<fU$, 
Our New Dress. 
THE YOUNG SCIENTIST was com- 
menced January, 1878, as a journal of 
twelve pages. The type was clear and 
handsome, but was a size larger than that 
I used in journals of a similar class— the 
object being to relieve the eyes of the 
reader as much as possible. The journal 
was essentially an experiment. It was de- 
voted wholly to pr^actical matters — eschew- 
ing theory as much as possible. Its ob- 
ject was to describe those facts in science 
which could be easily verified by exi)eri- 
ment, and to tell how to perform the ex- 
periment; and as a necessary adjunct ta 
this all those arts most affected by ama- 
teurs and young people formed important 
subjects for discussion. Our first idea was 
that twelve pages per month would be 
ample, but ere long we found that ad- 
ditional pages became necessary, and to- 
wards the close of the year the range of 
subjects in which our subscribers showed 
an interest, and the amount of matter 
pressed upon our attention, demanded 
more room. We therefore not only added 
four pages, but reduced the size of the 
type — the result being that the amount of 
matter contained in the number for Janu- 
ary, 1879, was more than one-half greater 
than that contained in the number for 
January, 1878. The pages were also elec- 
