ih'rl 



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 tlie 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 



iss- 



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. 



I 



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 



