THE YOUNG SCIENTIST. 
13 
magnet, so that to redeem our promise 
to make a magnet out of a poker, all we 
have to do, is to tell our readers to hold 
it upright. But, unfortunately, the mag- 
netism is weak, and as soft iron does not 
retain the magnetism which is imx)arted 
to it, as soon as we change the position of 
the poker, the magnetism is weakened to 
such a degree that we can hardly detect 
it. By the following method, however, 
we can easily make a permanent magnet 
out of a small piece of steel. 
Such a piece of steel is easily procured ; 
a piece of an old iile answers very well, 
but a piece of well-worked steel which has 
been made as hard as possible, is neater 
and better. Having procured such a piece 
proceed as follows : 
Take a poker and tongs, or two bars of 
iron, the larger and the older the better, 
and fixing the poker upright, hold to it 
with the left hand, near the top, by a silk 
thread, the bar of steel, of which the 
magnet is to be made, the marked end 
being downwards. Then, grasping the 
tongs with the right hand, a little below 
their middle as shown in the figure, and 
able it to lift a small key at the marked 
end ; and being suspended by its middle^ 
or made to rest on a point, this end will 
turn to the north, and is called its north 
pole ; the unmarked end being the soath 
pole. 
I 
MAKING A MAGNET WITH A POKEK AND TONGS. 
keeping them nearly in a vertical line, 
let the bar be rubbed with the lower end 
of the tongs, from the marked end of the 
bar to its upper end. about ten times on 
each side of it. By this means the bar will 
receive as much magnetism as will en- 
How to Hang" a Tliermometer. 
The recont cold weather has called general 
attention to this subject. The great differ(^uces. 
in the readings of thermometers hung up a 
short distance from each other, show either that 
tho majority of thermometers are incorrect, or 
tliat they have not been subjected to the same= 
influences. In greneral, the temperature that 
we desire to get is that of the surrounding air> 
T(30 often, however, we get the temperature of 
the clear sky, or of some wall or building whick 
is either much colder or much hotter than the 
air. Tlie temperature of the wall of any building-,, 
at any hour of the night or day, is not the true^ 
temperature of the circulating air, and is of no 
use to science. A wooden wall becomes cold 
more rapidly than one of brick or stone, and the 
amateur scientist who hangs his thermometer 
on a wooden wall can force liis mercury down 
below the amateur who selects a brick wall.. 
The proi>er way to expose a thermometer is to 
surround it with a light wooden frame, covered 
witli slats, like shutter work, and roofed over„ 
This will ijrotect it from the direct rays of the 
sun and reflected heat. Kun a light bar of wood 
across the centre of your shelter, to which the 
thermometer may be attached. This should 
be on the north side of the building, and at least 
one foot from all surrounding objects. 
The effect of a clear sky during a cold night ini 
depressing the thermometer, is something extra- 
ordinary. A simple screen of cloth placed be- 
tween the thermometer and the sky, though at 
some distance from the former, will make a dif- 
ference of several degrees in the result. Fortu- 
nately the bright bulbs of ordinary thermome- 
ters do not radiate heat very rapidly, and so the 
effect of this influence is not felt as severely as. 
it might otherwise be. But if we blacken the 
bulb so as to increase its radiating power, and 
then expose it to a clear sky, the fall will be^ 
something remarkable. 
The fact that the bulb of the thermometer, in^ 
its usual bright condition, neither radiates or ab- 
sorbs heat rapidly, is a most valuable and im- 
portant one. It is best seen in the case of the 
rays of the sun falling quickly on the bulb. 
Ordinarily this makes a chang-e of but a few de- 
grees— 15 to 30 at the most. But when the bulb 
is blackened, a difference of 100° to 150° may be 
seen between shaded and unshaded thermomc- 
