THE YOUNG SCIENTIST. 
99 
to put the work together, an undertaking 
that the boys had looked forward to with 
considerable anxiety for some time. The 
back was glued together, and the posts 
driven on to the edges of the back ; next, 
the turned rod was glued into the upper 
Fig. 47. 
brackets, and tlie latter were then screwed 
and glued to the posts. Then the shelf 
was fastened from the back, and the lower 
brackets and feet attached and properly 
fastened ; and lastly, the turned ornaments 
were glued and then driven in their places, 
and for the first time the "Umbrella 
Stand " stood on its feet. To Jessie, who 
had watched the operation throughout, 
the result seemed like a piece of magic, 
and her eyes fairly gleamed with astonish- 
ment. The boys, too, felt as though they 
had achieved something wonderful, and 
felt more important than ever they did 
before. Of course Mamma had to be in- 
formed of the result, and Jessie performed 
that duty almost instanter. 
"Now, boys," said Mr. Carpenter, "we 
will let our work stand Tintil to-morrow 
night, before we do any more to it, and by 
that time the glue will be ' set,' and then 
we will finish it ; so let us leave work for 
to-night." 
. • . 
Common Telescopes.— IV.^ 
THE MODE OF OBSERVATION. 
T>RASS-WOEK should not be rubbed 
^ with polishing powder, which might 
injure the lacquering ; ammonia is prefer- 
able. 
3. If the telescope does not seem alto- 
gether right, notwithstanding all the 
*From advance sheets of "Webb's Celestial 
Objects for Common Telescopes." 
pains you can take in bringing it to focus, 
do not meddle with screws or adjustments, 
unless you thoroughly understand the 
construction, or can obtain good direc- 
tions. In most cases a screw driver is a 
dangerous tool in inexperienced hands. 
4. Do not use any part of a telescope or 
stand roughly, or expose it to any blow 
or strain. It is a delicate instrument, and 
well deserves careful preservation. 
5. Do not spare trouble in adjjisting the 
focus. It is well known that different 
eyes require a change, sometimes a great 
one ; and the same observer's focus is not 
invariable, being affected by the tempera- 
ture of the tul^e and the state of the eye, 
the adjustment of w^hich, as Dawes has 
pointed out, shortens with intense gazing, 
and is apt to vary with the relative bright- 
nesses of objects, besides being, to a 
certain extent, under the observer's 
control. 
6. Do not over-press magnifying power. 
Schroter long ago Avarned observers 
against this natural practice, wdiich is 
likely to lead beginners into mistakes. A 
certain proportion of light to size in the 
image is essential to distinctness; and 
though by using a deeper e^^e-piece w^e 
can readily enlarge the size, we cannot 
increase the light so long as the aperture 
is unchanged ; while by liigher magnify- 
ing we make the inevitable imperfection 
of the telescope and the atmosphere more 
visible. Hence the picture becomes dim 
and indistinct beyond a certain amount of 
power, varying with the brightness of the 
object, the goodness of the telescope, and 
the steadiness of the air. Comets and 
nebulae, generally speaking, will bear but 
little magnifying. For the moon and 
planets, the power should be high enough 
(if the weather is suitable) to take off .the 
glare, low enough to preserve sufficient 
brightness and sharpness ; the latter con- 
dition being preserved, minute details are 
likely to come out better with an increase 
of power. Stars bear much more magnify- 
ing, from their intrinsic brilliancy ; and 
they are enlarged very slightly in propor- 
tion ; their images ought never, with any 
power, to exceed the dimensions of minute 
discs— spurious discs, as they are termed, 
arising from the undulatory nature of 
