190 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



Wireless Telephony from Ship to Ship. 



Here, of course, wireless telephony occupies a unique position. 

 Wireless telegraphy has the disadvantage that a telegraph operator 

 must be carried. The additional expense is an objection in many 

 cases. The proposition that the captain or mate should also be a tele- 

 graph operator has not met with favor. Anybody, however, can 

 operate the wireless telephone and almost every vessel carries an 

 engineer capable of repairing the electrical apparatus in case of acci- 

 dent. The final arrangement will, I believe, be this; that passenger 

 vessels will carry a telegraph operator and use the telephoning appa- 

 ratus for ordinary work and for telegraphing wdiere it is desired to 

 communicate over long distances. Other vessels will use the tele- 

 phone alone. 



Wireless TELEPHON.r. from Ship to Local Exchange. 



This also will, I think, have considerable value, as enabling the 

 captain of a vessel to communicate, by relaying over the wire line, 

 with the owner of the ship, or enabling a passenger on a vessel to 

 communicate with friends on shore. 



Range of Wireless Telephony, 

 atmospheric absorption. 



The great obstacle to long distance wireless telegraphy and te- 

 lephony is atmospheric absorption. For short distances up to 100 

 miles in the Temperate Zone there is little difference between the 

 strength of the signals at one time of the day and another. As soon as 

 the distance is increased much over 100 miles for the Temperate 

 Zones and 40 or 50 miles for the Tropics the signals at night are very 

 irregular and there is great absorption during the daytime. The 

 daylight -absorption may be so great that less than a tenth of one 

 per cent of the energy transmitted gets through. Some nights will 

 be as bad as daytime, while on other nights there will be apparently 

 no absolution. 



Figure 7 is a curve showing the strength of the messages trans- 

 mitted between Brant Rock, Massachusetts, and Machrihanish, Scot- 

 land, at night, during January, 1906. Nothing at all was received 

 that month during daytime. 



The change in the strengih of the signals is very sudden. In 

 working from Brant Rock to Porto Rico, a distance of 1,700 miles, 

 the strength of the signals with short wave lengths would fall off to 

 one one-thousandth of their former value during a period of less 

 than fifteen minutes, while the sun was rising. 



Early experiments showed that the absorption was greater as the 

 wave length was increased and the effect was at first attributed to 

 absorption in the neighborhood of the sending station, and was 



