The hour circle A is half of a similar card with the hour marks divided into 20 minutes.  An index pointer is fastened to the base of the polar axis.  A pointer 12 in. long is fastened with a small bolt to the center of the declination circle.  A small opening is made in the pointer into which an ordinary needle is inserted.  This needle is adjusted to the degree to set the pointer in declination and when set, the pointer is clamped with the bolt at the center.  A brass tube having a 1/4-in. hole is fastened to the pointer.

The first thing to do is to get a true N and S meridian mark.  This can be approximately obtained by a good compass, and allowance made for the magnetic declination at your own place.  Secure a slab of stone or some other solid flat surface, level this and have it firmly fixed facing due south with a line drawn through the center and put the equatorial on the surface with XII on the south end of the line.  Then set the pointer D to the declination of the object, say Venus at the date of observation.  You now want to know if this planet is 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.