THE YOUNG SCIENTIST. 
63 
and close to 20, is a small ampitheatre (21), 
having walls of the same height as 20, but far 
more precipitous; it is called Bernouilli. To 
the right or west of 21, and very close to the 
limb of the Moon at full, is Gauss (22), a very 
conspicuous object near sunset, when the 
shadow of its mighty wall on the west is thrown 
across the interior plain, enshrouding the base 
of its central mountain, while the inside of the 
eastern wall is bathed in sunset's golden rays ; 
it is 110 miles long. 
Endymion (27), Atlas (28), and Hercules (29) are 
three large walled plains, situated about 32^ 
from the north lunar pole in the N. W. Quadrant. 
27 is 78 miles in diameter, and its irregular wall 
in some places more than 15,000 feet, " overtop- 
ping all but the very highest peaks of the Alps." 
It is best seen 3d. 7h. after New, and 2d. 9h. after 
Full. Atlas is a grand ampitheatre 55 miles 
broad, containing 460 square miles. Its ring 
rises on the north 11,000 feet, and is exceedingly 
rich in terraces and towers. A small and very 
dark spot is near the centre. Hercules is the com- 
panion of Atlas, being only a few miles east. It 
is 46 miles across, and the ring is double in 
.places. Best seen 5 or 6 days after New, or 3| 
days after Full. 
South of these are several incomplete rings, all 
opening northward. At the right of 27, Mare 
Humboldtianum (B) forms part of the W. Limb, 
and the peaks of its border sometimes appear 
in profile 16,000 feet high. 
Penn Yan, N. Y. 
What Old Triangular Tiles Can be Used 
For. 
Teiangulae files when worn, are generally 
thrown aside as worth but very little except for 
old steel, but their sphere of usefulness need not 
-end here. 
Probably one of the most curious uses to 
which such a file can be put is that it can be 
I made into a very good glass cutter. Grinc the 
I three sides at the point smooth, so that the 
teeth are obliterated. Grind the sides flat, but 
shape the point curved or convex. To use it, 
! hold the tool so that one of these sharp rounded 
edges will bear upon the glass, and with a little 
■pressure, draw it steadily over the glass. The 
result is a slight scratch or cut, and by using a 
little force the glass will break where this 
■scratch is seen. 
If the teeth of an old file be removed by grind- 
ing, and the taper shape be preserved, it will 
make a passable hand reamer. If the point be 
made obtuse or " stunt," it forms a convenient 
•substitute for a hand countersink. If the tool is 
put in a hole that is to be enlarged it will be obr 
served that there is an equal bearing at the 
three points, which gives a steady hold on the 
metal to be removed. Now turn the tool a little 
so that it will cut. Observe the position and 
shape of this cutting edge. To the initiated it 
will present about the same form as that of tlie 
cutting edge of the tool used by the machinist 
to cut iron in the lathe. 
The form of the file being three-square, or 
triangular, the edges present an angle of 60 
degrees. This is the strongest and best angle 
known to cut iron and the hard metals. This 
same angle is used by the machinist to shape 
the points of his lathe centres, and also to make 
the indents in shafting and the work to be put 
on these centres to be turned. It may also be 
mentioned that screw-threads, when correctly 
made, have this same angle. It may very pro- 
perly be called " the angle of strength." 
As a scraping tool to remove an amount of 
metal in a short space of time, the old file, when 
properly ground, has no equal. It can be used 
to scrape out curves and hollows and finish 
rounds and swells. No other shaped tool would 
answer as well. 
If ground after the manner of a graver, the 
old file can be used as that instrument, answer- 
ing all that may be required of it, being capable 
of producing much good work. 
As a hand turning tool for working iron, brass, 
ivory, bone, the softer metals as well as the 
harder woods, it makes a most excellent tool. 
One form may be made by grinding the sides 
smooth and making the point sharp. The tool 
then presents three cutting edges, and serves 
some of the purposes of the diamond-pointed 
tool. If the file be ground at the end with three 
obtuse cutting edges, it can be used precisely 
like the diamond-pointed tool, and is very strong 
and durable for cutting metals. If the file be 
broken off square and only one cutting edge be 
made across the broken end, it will make a use- 
ful turning tool for some purposes. 
One great advantage in using old files of this 
kind for tools is that the file is already made and 
shaped to receive the handle, and is tempered 
the entire length to the commencement of the 
tang. Eenewing by grinding will produce a 
cutting edge with no occasion to harden and 
temper. Its cost to be made into a very good 
tool is very little. As a general thing, otlier 
tools are tempered but a short distance from 
the cutting edge, and after being used enough 
to have this worn or ground away, the temper 
must be renewed. 
In selecting old files for tools it may be borne 
in mind that as a general thing coarse-cut files 
or files with coarse teeth are make of a grade 
of steel not so fine as those that are made with 
fine teeth. As a hint to get a good tool, select 
an old file that is cut with fine teeth.—Black- 
smith and Wheelwright. 
