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��Popular Science Monthly
��dcicctor-protecting switches may be omit- ted at the receiver. A loading-coil will be necessary, but since it is to be used for receiving only it may be made as described in the Se[nember article instead of highly insulated in accordance with the October description. The transmitter should be connected as shown in October, and the receiver should be wired as in Fig. 3. The comments in this article as to the adjust- ment will still apply, except that the two switches need not be considered.
The receiving apparatus described here will work one mile easily, and is capable of hearing signals much farther away. In the next article an adjustable receiving set will be discussed, by the use of which signals may be heard from stations located hundreds of miles away.
��A Salt Water Polarity Indicator Made from a Burned-Out Fuse
A POLARITY indicator which will de- termine the positive and negative poles of a direct current line or a battery can be made from a burned-out electric fuse of the cartridge type, a glass tube and two corks. The glass tube, which fits snugly within the fiber cartridge, is cut the same length as the cartridge and a small slot is cut through the fiber as indicated in the drawing.
Short lengths of copper wire should be forced through holes Ijoretl in corks which fit tightly into the ends of the glass tube. A diluted solution of salt and water is. poured in when one cork is fitted ; then the
���A glass tube with copper wire run through its two corks fits inside the cartridge
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��The prepared glas in pl.H (■ in llu' car-
��other is put in place, filled tube is then pul tridge.
When thewirc terminals are connected to fi tlirect current, the negative pole will be indicated by bubbles rising from one of the cofjper i)lugs. The opening in tin- fiber permits the bubbles to bi- plainly seen as they rise. — M. K. Gordon, Jk.
��An Electrically-Operated Recording Weather Vane
N YACHT clubs, in laboratories of some sorts, on the farm and other places nimierous beyond mention, it is often desirable to know for instant con- venience the exact direction of the wind.
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���JaIR 5PACE^'
FRONT INDICATOR DIAL -
��LAMPS -
��Dial and electric segments for showing the wind's direction inside of a house
In the day-time this information is some- times difficult to secure owing to the fact that the weather vane is perched on the roof of a building out of convenient eye range. Night necessarily increases the diflfculty.
An electric weather vane which will indicate the direction of the wind on a dial comeniently located can be constructed easily. The compass, in the first place, is divided into eight parts, or directions: N, NE, E, SE, S,'^SW, W, and NW. On the weather-vane dial described, if the wind should be blowing in a direction between two of those indicated — for instance, north- east by north, the two directions, north- east and north will be indicated. Conse- quently, the vane will register 16 points of till' compass instead of only 8 as might be inferred at first thought.
A specially designed weather vane should be erected on a high roof. No vane will register accurately utiless it is at a higher altitude than the Iniildings in the immediate \icinity. This vane consists of the usual light arrow which is pi\oted at its center of balance. It can be <)uickh- made from a shingle, sawed or whittled in the sh.ipe of an arrow, as in<li(aled in one ol the draw- ings, and then well covered with weather- proof paint or varnish.
The pivot consists of a ],«-\n- round brass rod which passes through a close fit- ting hole in the lop of a seasoned wood
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