128 



THE WORLD'S ADVANCE 



geous to work with this disk speed and 

 condenser. 



The first indication that impact exci- 

 tation is taking place is the tight coup- 

 ling required for maximum antenna cur- 

 rent and also the large drop in this maxi- 

 mum which accompanies the slightest 

 change in coupling from this critical po- 

 sition. The conditions can be more ac- 

 curately analyzed by loosely coupling a 

 wavemeter circuit to the antenna. The 

 resonance curve (i) of Fig. 6 was taken 

 on an antenna of 0.002 mf . capacity at a 

 wave length of 850 meters with the eight 

 gaps in series. The curve (2) of Fig. 6 

 was taken under exactly similar condi- 

 tions, except that only two gaps were 

 used. The wavemeter circuit contained 

 a rotary variable condenser of maximum 

 capacity about 0.004 mf. and an induc- 

 tance of about 100,000 cms. The self- 

 damping of the wavemeter circuit at the 

 wavelength employed was 0.02. The 

 coupling of the condenser circuit to the 

 antenna was adjusted, in each case, for 

 maximum aerial current. The maximum 

 readings of the ammeter in the wave- 

 meter circuit are not to be compared 

 among themselves as a measure of the 

 energy in the antenna, because the coup- 

 ling between the wavemeter and the an- 

 tenna was varied from time to time. As 



far as the aerial current alone is con- 

 cerned, the use of the eight gaps gave 

 readings from 20 per cent, to 30 per cent, 

 higher than those obtained with two gaps. 

 In conclusion, it has been found that 

 this series gap exhibits properties ap- 

 proaching those of impact excitation. 

 This is due, at least in part, to the inher- 

 ent cooling properties of the rotary gap 

 and to the favorable relation of arc volt- 

 tage to spark voltage in series gaps. The 

 proper selection of a spark gap alloy is 

 of importance. In this connection zinc 

 is one of the so-called non-arcing metals, 

 and in general its addition to an alloy 

 renders the alloy non-arcing. It has been 

 found, however, that zinc becomes pitted 

 in the electric spark, and hence it is of 

 advantage to alloy it with copper whose 

 tendency to "bead" counteracts the pit- 

 ting tendency of the zinc, and results in 

 an even wearing of the gap surfaces. 

 The series rotary gap, in the present case, 

 gives an improved power factor on the 

 transformer and an increased overall ef- 

 ficiency into the antenna with lower aeri- 

 al decrement. The motor speed was in- 

 variable in these experiments; it is be- 

 lieved that a higher speed than that used 

 will magnify the advantages of the gap, 

 and experiments to verify this are con- 

 templated for the near future. 



CENTRAL RADIO ASSOCIATION 

 BLUE BOOK 



The Blue Book published by the Cen- 

 tral Radio Association is now ready for 

 distribution. Not only does this book 

 contain a list of stations of all the mem- 

 bers of the association, which covers 

 nearly thirty states, but it also contains 

 numerous wireless facts. The sending 

 power, make of coil or transformer, 

 transmitting distance and other interest- 

 ing data cf every station listed, is also 

 included. In addition to the list of mem- 

 bers the call letters of several hundred 

 amateurs who hold a Government li- 

 cense, but who have not yet joined the 

 association, are given. 



The Blue Book contains a full explana- 



tion of the Government time signals and 

 weather forecast code, an illustrated ar- 

 ticle on the construction and operation 

 of the audion detector and amplifier, a 

 list of all the principal land and naval 

 stations and their call letters, the abbre- 

 viations authorized by the International 

 Radio Telegraphic Convention, as well 

 as a list of abbreviations in general use. 

 A page has been devoted to a key to the 

 call stations of the world, enabling an 

 operator to locate the origin of any un- 

 known official call. In addition to these 

 features there are a number of articles 

 of general interest to the members of the 

 association. 



A copy of the Blue Book will be 

 mailed to any one upon the receipt of 

 fifty cents. Correspondence should be 



