THE YOUNG SCIENTIST. 
It will be noticed that, as in terrestrial maps, 
North is at the top and South at the bottom of 
the map, but East and West are reversed ; that 
is, East is at the left and West at the right. 
Hence, when observing the Moon and using a 
terrestrial eye-piece, it will appear as represented 
in the map ; but while using an inverting eye- 
piece and comparing, the map should be in- 
verted, so that S. will be at the top and N. at the 
bottom, then W. will be at the left and E. at the 
right. 
The First Meridian and Equator are the only 
great circles represented, and these divide the 
map into four quadrants, which are called the 
1st or NW., 2d or NE., 3d or SE., and 4th or SW., 
Quadrants. 
Nothing is to be gained by the use of high 
powers. A good telescope, with a clear aper- 
ture of three inches, ought to bear a power of 
450, and it will be found that nothing can be 
gained by the use of higher powers. Indeed, for 
most purposes in lunar observations, a much 
lower power is preferable. 
Very much depends upon the age of the Moon 
at the time of the observation, as many remark- 
able features which are plainly visible at certain 
times or at a particular age of the Moon, are 
either wholly invisible at the full or are very 
unsatisfactory. Hence, in future articles, we 
will instruct as to when to look for these things. 
It would be well to mount the map upon a 
piece of firm cardboard large enough to leave a 
margin of two inches all around, so as to have it 
in convenient shape for reference, and not dam- 
age it with finger marks. 
The writer will give careful attention to all 
letters of inquiry regarding telescopes, etc., 
which may be suggested by these articles. 
Penn Yan, N. Y. 
A Cheap Telephone. 
Ed. Young Scientist— To make a cheap and ser- 
viceable telephone good for three blocks or so, 
only requires enough wire and two cigar boxes. 
First, select your boxes and make a hole 
about half an inch in diameter in the cen- 
tre of the bottom of each, and then place 
one in each of the houses you wish to con- 
nect, then get five pounds of common iron 
stove pipe wire— you can take back what 
you don't use— make a loop in one end and 
put it through the hole in your cigar box and 
fasten with a nail ; then draw it tight to the 
other box, supporting it when necessary with 
stout cord. You can easily run your line into 
the house by boring a hole through the window | 
sash, or cutting a hole through the glass. Sup- ; 
port your boxes at their ends with slats nailed i 
across the window, and your telephone is com- ii 
plete. I have one that is two blocks long, and i 
cost forty-five cents, that will carry music when 
the organ is played thirty feet away in another 1 
room. There are quite a number of lines like 
this in town. Harky Holdbn. 
Black Earth, Wis. 
Examining the Bottoms of Ponds and • 
Rivers. 
Ed. Young Scientist— In the last issue of the | 
Young Scientist, there is a very interesting \ 
article on the use of mirrors for examining the ; 
bottoms of wells, ponds, and rivers. I have ' 
used mirrors for this purpose, and can endorse j 
all that is said of them. In the case of ponds . I 
and rivers, however, something more is needed 
as the reader will find if he tries. Some years 
ago, while fishing in a somewhat deep lake from 
a boat, I had the misfortune to lose a valuable 
little rifle. We marked the place pretty care- 
fully, buoyed it, as I believe the sailors call it, 
and tried to work out some plan by which it 
might be recovered. We even had thoughts of 
employing an expert swimmer to dive for it, 
but could not find one in the neighborhood. In 
this dilemma our old Professor of Natural 
Philosophy (of Physics he called himself,) came 
to our aid. He never was happier than when 
helping us boys, provided he could teach us at 
the same time, and you may readily believe that 
under such circumstances V7e were glad to learn. 
The Professor armed himself with a large mir- 
ror (it was at least two feet long and of propor- 
tionate width), a thick horse blanket, a large 
hoop from a hogshead, a powerful compound 
magnet, and some stout cord. When we reached 
the spot in the boat, the buoy was still there, 
and we anchored as close to it as possible. 
The Professor tied the magnet to the cord, 
and arranged the blanket over his head so that 
the ends dipped into the water and excluded all 
light except what came up through the water. 
The hoop enabled him to form a sort of tent, so 
that he had room to work. We had, of course, 
chosen a bright day, but alas for Old Probabili- 
ties, it clouded up just as we got afloat. This, 
however, did not seem to disconcert our Profes- 
sor. His original plan had been to throw the 
sun's rays to the bottom of the lake by means of 
the mirror, and he, being in total darkness, ex- 
cept for the light coming from the bottom of 
the lake, Avould be enabled to see any object 
lying there. Now, however, he took from his 
pocket a bit of magnesium ribbon, and we set it 
on fire outside his tent Of course we held it so 
