416 AUSTIN— ENERGY IN RADIOTELEGRAPHY. [April 19, 



tant observations during the Brant Rock test. Considering the diffi- 

 culties of taking these measurements, the agreement with the theo- 

 retical curve is all that could be desired. It is especially to be noted 

 that the signals became inaudible at almost the exact distance indi- 

 cated by the formula. 



Other Observations. 



Previous to the cruise of the Salem, a number of observations on 

 signals from Arlington were made in the daytime at various naval 

 wireless stations in the United States. The results of these are 

 shown in Fig. 4, the curve being as before the calculated value of 

 received current over sea water, and the crosses the observed values 

 at the various points. It will be noticed that while the observed values 

 uniformly lie below the calculated values, the differences are not as 

 great as would perhaps naturally be expected in transmission over- 

 land. In fact, they are in most cases not much greater than would 

 be accounted for by the circumstances of observation. The St. 

 Augustine observations are the only ones which were made by the 

 calibrated detector and galvanometer method, while those at New- 

 port, Boston, Guantanamo, Charleston and Key West were taken on 

 uncalibrated crystal detectors by the shunted telephone method. The 

 results show that for a wave-length of approximately 4,000 meters 

 the ground absorption is small, at least for distances less than 1,000 

 miles. This is a very different result from that obtained with a 

 1,000 meter wave-length between New York and Washington, where 

 the received current in the summer time is reduced to 10 per cent, 

 of the value which it would have over salt water.^^ Of course, -it 

 must be considered, in the Arlington experiments just mentioned, 

 that most of the stations lie on the sea coast so that the waves either 

 pass during a portion of their course over water or might be con- 

 ceived to follow along the shore rather than to pass in direct line. 

 New Orleans is the only station in which the propagation could be 

 considered to be entirely unaffected by the sea, and in this case the 



"For great distances over sea, and distances of more than 100 miles over 

 land, long waves should be used on account of their decreased absorption; 

 while for short distances shorter waves are better on account of their more 

 vigorous radiation. 



