628 



across the secondary winding will break 

 down whenever the vibrator is starte<l 

 buzzing, and a singing, clear spark will 

 jump across as long as the key is held 

 down. 



Popular Scirncr Monthly 



at C. Four yi-'m. holes are then bored 

 in each, at points a little less than 2 in. 

 from the corners, along diagonals as 

 shown in Fig. 4. Twelve porcelain 



5 



The Spark-Gap 

 spark-gap for the 



wireless 

 shown in Fig. 2. 



A good 

 sender can be made as 

 Two battery zincs, Z, Z', which can be 

 bought from any electrician, are cut off 

 to about 3 in. in length, leaving the' 

 connection screws at tlie head of each. 



s-^, 



FI6.2 



A spark gap made from two battery zincs 

 and a hardwood base boiled in paraffin 



Holes to fit these a trifle loosely are 

 bored through two stubby brass stand- 

 ards or pillars, P, P'. A smaller hole is 

 bored lengthwise through each pillar and 

 tapped to take a 10-24 machine screw, 

 such as 5 and 5', to clamp the zinc 

 electrodes in any position desired. Sim- 

 ilar screws, S^ and S^, pass upward 

 through counter-bored holes in a hard 

 rubl)cr base, B, and serve to fasten the 

 ]jillars in place. Hardwood boiled in 

 paraffin may be used for the base, but 

 rubber is better because it is a bettor 

 insulator. The ends of the zinc rods, 

 where they come close together, should 

 be filerl i)erfectly smooth and parallel. 



The Loading Coil 



It is essential to use a "loading coil" 

 with this outfit in order to get the best 

 results, and to make the transmitter 

 meet the rciiuircnicnls of the l<"ederal 

 laws governing the ojjeration of wireless 

 telegraph senders. This coil can easily 

 be made l)y following the suggestions 

 given in Figs. 3 and 4. Two square 

 boards, about 12 by 12 in. with rounded 

 corners, are first cut out of hardwood 

 about I in. thick. A hole |.f in. in 

 (li.iiiicler is drilled at the center of each, 

 and I oniiter-bored to about I in. in 

 diameter in the bottom of the baseboard 



Twelve 

 insulators of the sort shown in Fig. 

 are slipped over each of four yi-'m. 

 hardwood dowels, whose ends pass 

 through the yi-'m. holes just referred to 

 and are cut off (lush with the upper and 

 lower surfaces of the top and base. A 

 long ]/i-\n. brass bolt is passed upward 

 through the central holes, so that its 

 head drops into the counter-bored space 

 in the base and its threads project a 

 short distance above the top. A washer 

 and nut put on the upper end will then 

 hold the entire framework together. 



Some No. 10 bare copper wire, or 

 some stranded bronze tiller-rope or 

 aerial wire, is to be wound spirally on 

 the insulators. Referring to Fig. 3, the 

 end is first wrapped around the upper 

 front right-hand insulator A and spliced 

 on itself. Tlie wire is then led straight 

 back to the toji insulator of the back 

 right upright, then across to the top 

 back left insulator, as shown by the 

 dotted line, then forward to the top 

 front left insulator, and then to the ne.\t 

 lower front right porcelain. The winding 

 is continued as shown until the last 

 insulator, B, is reached; there the wire 

 is made fast by splicing, as before. 



Two connected clips must be made or 

 purchased. The spring testing cli])s sold 

 by electrical su|iply houses are admirable 

 for tliis, thougli anything of the sort will 



Fie.3 



A loading coil to make the transmitter meet 

 Uic requirements of the federal laws 



do. I'^lexible wires are soldered to each 

 of them, so that connection to any part ol 

 I lie bare wire-spiral may be maile merely 

 by clipping on the ilesin-jl point. 



