A large gate hinge is used to hold the pedal to the
floor.
--Contributed by Edward Whitney, Madison, Wis.
[Illustration: Furnace Door Opener]
** How to Make an Efficient Wireless Telegraph [84]
By GEORGE W. RICHARDSON
A simple but very efficient wireless telegraph may be constructed
at slight cost from the following description:
The sending apparatus consists of nothing but an induction coil
with a telegraph key inserted in the primary circuit, i. e., the
battery circuit. This apparatus may be purchased from any
electrical-supply house. The price of the coil depends upon its
size, and upon the size depends the distance signals can be
transmitted. If, however, one wishes to construct his own coil he
can make and use, with slight changes, the jump-spark coil
described elsewhere in this book. This coil, being a 1-in. coil,
will transmit nicely up to a distance of one mile; while a 12-in.
coil made on the same plan will transmit 20 miles or even more
under favorable conditions.
Change the coil described, as follows: Insert an ordinary
telegraph key in the battery circuit, and attach two small pieces
of wire with a brass ball on each, by inserting them in the
binding-posts of the coil as shown at B B".
Pages:
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210