abstracts: radio-telegraphy 83 



oped 60 kw. Its antenna was an umbrella 420 feet at top, about 170 feet 

 at bottom with a capacity of 0.0073 microfarad. The scouts' sets were 

 of 10 k.w. and their antennas were flat-topped, 130 feet high, with a 

 capacity of 0.0018 microfarad. During a part of the test this was 

 increased to 0.0025 by extensions slanting downward fore and aft of 

 the regular antenna. The chief wave lengths used were 1500 meters 

 and 3750 meters on the part of Brant Rock, and 1000 meters and 

 3750 meters on the ships. 



In the July, 1910, test which was considered the most reliable the 

 measurements were carried on up to nearly 900 nautical miles between 

 the ships and to about 1200 miles between Brant Rock and the Bir- 

 mingham. 



The receiving measurements for the shorcei distances were made in 

 part by means of thermoelements in the antenna. At the greater dis- 

 tances the method of telephone shunt readings in connection with the 

 electrolytic detector was used, the value of the received antenna current 

 being derived from the shunt reading by means of comparison readings 

 taken on a thermoelement in the antenna at the shorter distances. 



In addition to these measurements already mentioned subsidiary 

 observations were made between Brant Rock and a small station 11 

 miles away on the effect of height of a flat top antenna on sending and 

 receiving and also on the effect of wave length. 



The results are briefly as follows : 



(a) Over salt water the electrical waves decrease in intensity in pro- 

 portion to the distance as found by Duddell and Taylor. In addition 

 they are subject to an absorption which varies with the wave length 

 and which may be expressed mathematically by the term e~ Ad . 



The complete expression for the received current is then 



(1) I R =4e- Ad 

 d 



where I R is the received antenna current, d the distance, and K and A 

 constants. 



This is true in general for day transmission. The absorption at night 

 is entirely irregular varjing from zero to the day value, but is on an 

 average much less during the winter than in summer. The great varia- 

 tions in night absorption make useless all attempts to judge the quality 

 of wireless apparatus from night distances. For this purpose only ob- 

 servations on the average day range have any value. Variations also 

 appear to occur during the daytime, but these are probably in general 



