s east or west of your meridian at the time of
observation. The following formula will show how this may be
found. To find a celestial object by equatorial: Find the planet
Venus May 21, 1881, at 9 hr. 10 min. A. M. Subtract right
ascension of planet from the time shown by the clock, thus:

hour minute second
9 hr. 10 min. shows mean siderial. 1 0 0
Add 12 hrs 12
--- --- ---
13

Right ascension of Venus 2 10
--- --- ---
Set hour circle to before meridian 10 50 0
Again------------------
At 1 hr. 30 min. mean clock shows 5 20 0
Right ascension of Venus 2 10 0
--- --- ---
Set hour circle to 3 10 0

Books may be found in libraries that will give the right ascension
and declination of most of the heavenly bodies.

The foregoing tables assume that you have a clock rated to
siderial time,

[Illustration: Home-Made Equatorial]

but this is not absolutely necessary. If you can obtain the
planet's declination on the day of observation and ascertain when
it is due south, all you have to do is to set the pointer D by the
needle point and note whether Venus has passed your meridian or
not and set your hour index. There will be no difficulty in
picking up Venus even in bright sunlight when the plant is visible
to the naked eye.

** Electric Light Turned On and Off from Different Places [205]

How nice it would be to have an electric light at the turn in a
stairway, or at the top that could be turned on before starting up
the stair and on reaching the top turned out, and vice

[Illustration: The Wiring Diagram]

versa when coming down. The wiring diagram as shown in the
illustration will make this a pleasant reality. This wiring may be
applied in numerous like instances. The electric globe may be
located at any desired place and the two point switches are
connected in series with the source of current as shown in the
sketch. The light may be turned on or off at either one of the
switches.
--Contributed by Robert W. Hall, New Haven, Conn.

** How to Make a Bunsen Cell [206]

This kind of a cell produces a high e.m.f. owing to the low
internal resistance