38 
THE YOUNG SCIENTIST. 
Pull Moon, or about the llth and 27th of April. 
Mare Crisum may be seen with the naked eye 
as a dull greyish patch. With the telescope it 
appears oblong with a brighter ring. On the 
27th the northern horn of the crescent partially 
intersects it, and is partially covered with the 
shadows of the high mountains upon the north- 
east side, some of which are estimated to be 
16,000 or 17,000 feet high. This vast plain is be- 
lieved to be a "dry Hat," analagous to our 
deserts. 
Mare Crisum is 280 miles from N. to S., 354 
from E. to W., and contains 14,260 square miles, 
or 1-lllth of the Moon's visible hemisphere. By 
some observers it is thought to contain a trace 
of green, possibly, though not probably, due to 
periodical vegetation. The surface is more 
deeply depressed than that of Mare Foecundi- 
tatis (X) or Mare Tranquillatatis (G). Some of 
its boundary mountains are very steep and high. 
Promontorium Agarum (1) rises 11,000 feet, and 
the peak S.E. of Picard (4) 15,600 feet. The last- 
named crater is within Mare Crisum, as will be 
seen, and it is recorded by some observers that 
regular, white ridges, like walls, are just South 
of Picard. 
Near the E. edge a low spot may be seen in the 
surrounding ridge, forming a pass, and near it 
are several mountains, some quite lofty. Some 
observers believe that they have noticed changes 
in these. The craters in this district seem to 
lack the little central hills so common in the 
< others. 
A strange story is told of an observation made 
on this sea by a pupil of the astronomer, Lam- 
bert; it is as follows : The night was perfectly 
clear, and with a common 4 feet refractor he 
saw four bright spots in Mare Crisum, two of 
which are now known. After noticing them for 
two hours he found, all at once, that the part of 
the terminator, or horn of the crescent, in M. 
Crisum, had a slow reciprocating motion, oscil- 
lating between the pairs of black spots in five or 
six minutes. The same phenomenon was ob- 
served with larger and smaller telescopes. A 
similar occurrence has been noticed in the case 
of Jupiter's satellites, during transit, and with 
stars when about to be occulted by the Moon. 
It seems to be some kind of an optical illusion 
which has never been satisfactorily explained. 
Penn Yan, N. Y. 
On Drills and Drilling. 
The attention of many professional men and 
others interested in mechanical operations has 
for a lengthened period been directed to this 
subject. As must be well known, there are a 
^reat many descriptions of drills now in use- 
some good some indifferent. The American 
twist-drills are now sold in large quanties, and 
for some purposes answer exceedingly well; 
but at the same time there are points to be 
reckoned against them. Firstly, it is very dif- 
ficult to grind both edges at the same angle, and 
if this is not done, the result will be that the hole 
will not be the true size of the drill used ; this 
will deceive a workman, and may probably spoil 
good work. And another objection to them is, 
that when the drill is about to come through 
the hole being bored, the quick twist causes it 
to worm through at such a speed that, in many 
cases, the drill is either broken, or the work 
forced up to the end of the twist, thus spoiling 
what might otherwise have been a smooth hole. 
We consider that the best description now in use 
is the straight fluted drill, which was originally 
introduced by a Mr. Martin, of Charlton ; but 
this gentleman having for some long time 
ceased to make them, there arose a difficulty in 
procuring them. They are now, however, to be 
had more readily, and a set of these drills should 
certainly be found amongst the tools in every 
workshop. 
With all the improvements that have from 
time to time been introduced in the various 
drills, in most factories, we have frequently 
noticed, that except for very large work, every 
workman prefers to make his own drills, and 
from personal experience we have found no 
better drills than those thus made, to do which 
is a simple process. For example, a drill-chuck 
being fitted to the lathe, with a round hole 4 in. 
in diameter, and a fixing-screw ; have always 
at hand a bar of round cast steel of the correct 
diameter, to fit the hole, and cut off a length as 
required. If the drill is to be made of a large 
diameter, it must be flattened out at the forge 
to the desired size, and then finished with a file. 
Most workmen, nowadays, simply forge their 
drills and grind them into shape ; this answers 
every purpose for work that does not require 
any finish, all that is necessary is that the tool 
should run pretty true in the lathe and cut well. 
In boring a hole in thin work it becomes neces- 
sary to make it flat at the bottom. To do this 
a small half-round bit placed in the same chuck 
answers the purpose. This is essential where 
the hole has to be topped, as it allows of one or 
two more threads being made by the top. If 
the drill is required to be smaller in diameter 
than the steel from which it is made, it is a 
simple matter to turn down the end and then 
file it flat on both sides, to the same shape as 
the larger one previously mentioned. A great 
point with regard to drilling is the hardening of 
the drills. The old-fashioned cylinder-bit for 
finishing a long hole is as good as any. To 
