478 



Popular Science Monthly 



depend upon the electrical contact in the 

 bearing of Fig. 9 alone; a small piece of 

 thin spring wire (brass or phosphor bronze) 

 should have one end soldered to the shaft 

 just above the upper plate of the base 

 bearing, its other end being fastened to the 

 bearing itself after one or two spiral turns 

 are made loosely about the shaft. This will 

 prevent any possible trouble from oxidation 

 of the contacts within the condenser. A 

 stop should be provided to keep the plates 

 from turning more than 180 deg. and 

 twisting off the spring wire. 



Assembling and Adjusting 

 Manifestly the foregoing descriptions, 

 with reference to Fig. 6, 7, 8 and 9, apply 

 to the completed apparatus. The best way 

 to assemble the instrument is to clamp to- 

 getft^r the fixed plates on their four rods, 

 independent of either the base or top plates 

 of insulating material. When the conduct- 

 ing plates are all set parallel and with the 

 proper 3^-in. spacing, they are laid aside and 

 the moving plates similarly assembled upon 

 the shaft. The base, hand wheel and top 

 are left apart until the moving plates have 

 been correctly spaced and adjusted. Then 

 the moving plates are slipped interleaf- 

 wise between the fixed plates, and the insu- 

 lating top put in place. By trial the proper 

 number of washers and the best position 

 of the clamping nuts is determined, and the 

 top is then fastened. Next the base is ad- 

 justed to the proper position, and all the 

 fastening nuts tightened. Last of all the 

 hand-wheel and pointer are added, and the 

 scale set to the correct position. It is a 

 good plan to cut a strip of celluloid film 

 to just the width of the space between the 

 insulating top and base, and to bend it 

 around the metal parts so as to exclude 

 dust. When this is to be done, the top and 

 base may be made 5}4 in. square to give 

 a little additional edge-space in which the 

 celluloid strip may be fastened by gluing 

 bits of 3^-in. felt next to it. 



The next article of this series will de- 

 scribe fully the use of the variable con- 

 denser in the sharp-tuned secondary, as 

 well as methods of adjusting the primary 

 circuit by using the same instrument. 



An Easily Erected Antenna for 

 Wireless Operators 



ABOARD ships it is necessary to replace 

 . aerial wires at least once a year on 

 account of the action of the salt spray and 

 the smoke and gases from the stack. In 



constructing an aerial it is usual to secure 

 spreaders the proper distance apart and 

 stretch the wires between. This necessi- 

 tates the removal of the spreaders and their 

 holders from the ship to the wharf or clear 

 space where the work can be done, and 

 often requires the labor of from two to four 

 men for at least one day, depending, of 

 course, upon the size of the aerial. To 

 hoist the new aerial into place requires 

 another half day, with additional men to 

 assist in clearing the wires from davits, 

 funnels, etc. 



The aerial aboard a government vessel 

 had to be renewed recently under a guaran- 

 ty that the vessel would not be laid up, 

 that the radio apparatus would not be 

 kept out of operating condition for more 

 than one hour, and that the same spreaders 

 and attachments would be used. The pro- 

 cedure to meet these conditions was as 



Ordinary snaps used on 

 aerial lines to place them in 

 position quickly on a vessel 



follows: The phosphor-bronze antenna 

 wire was measured off into the required 

 lengths and a snap hook was fastened to 

 each end. Inasmuch as heat applied in 

 soldering this kind of wire invariably 

 weakens it and makes it liable to part 

 under strain at the point where the heat 

 was applied, soldering the joints was dis- 

 pensed with and patented sleeves or con- 

 nectors were used. This allowed also 

 greater speed in the construction. 



When all the wire work was complete 

 the old aerial was lowered to the deck and 

 the wires quickly cut away. The new 

 aerial was snapped into place and hoisted 

 aloft. The actual time required in making 

 the change was less than one hour, and the 

 services of three men were required to 

 hoist it in place. The making up of the 

 wires, hooks, etc., can be done by one man, 

 and by using this method an aerial can be 

 installed in one-fourth the time and with 

 only one-third to one-half the labor required 

 by the old method. — Frank M. Meals. 



