June 10, 1898.] 



SCIENGE. 



793 



carried on in the climatic conditions wliicli 

 render other modes of communication diffi- 

 cult, if not impossible, the experiment is 

 surely worth trying. 



Other possible applications of this system 

 of telegraphy might be enumerated, but it 

 can scarcely hope to come into general use 

 until one difficulty at least has been over- 

 come, that is, to ensure that a message is re- 

 ceived by the person to whom it is sent and 

 by no other. Electric waves are thrown off 

 in all directions from their generator, so 

 that if a man sets up a station all his mes- 

 sages can be read by any one who cares to 

 put up a precisely similar station within 

 the limits to which the waves travel. Two 

 principles may be employed to remove or 

 lessen this inconvenience. Electric waves, 

 like light waves, can be reflected and inter- 

 cepted ; hence a station could prevent the 

 emission of waves in every direction but 

 the one in which lay the station with which 

 it wished to communicate, and thus reduce 

 the possible eavesdroppers to those lying on 

 the line along which the waves were di- 

 rected. The other principle is that of syn- 

 tony. Just as one tuning fork will vibrate 

 in sympathy with another provided they 

 are in tune with each other, and not other- 

 wise, so one electric circuit will respond to 

 the oscillations taking place in another, if 

 they are in tune, but will be unaffected if 

 they are not. Two stations therefore can- 

 not telegraph across space to each other 

 unless their apparatus is syntonized ; hence 

 by adopting differences of tuning a certain 

 degree of secrecy may be arranged for. It 

 remains to be seen whether the application 

 of these two principles will suffice to pro- 

 vide a solution of the problem. 



CURRENT NOTES ON 3IETE0B0L0GY. 

 PHYSIOLOGICAL EFFECTS OF HUMIDITY. 



EuBNEB and Von Lewaschew have re- 

 cently been conducting laboratory experi- 

 ments with a view to determining the 



effects of different degrees of atmospheric 

 temperature and humidity on the human 

 body {Archiv. /. Hygiene, Vol. XXIX). 

 The individual on whom the experiments 

 were made was placed in a closed chamber, 

 into which air of varying known degrees 

 of humidity was admitted. The separate 

 tests lasted from four to eight hours each, 

 and one hour befoi'e every test the same 

 breakfast was eaten, while no food or drink 

 was taken during the experiment. The 

 body and the clothing were weighed before 

 and after each trial, so that the amount of 

 moisture given off or absorbed might be 

 known. It was found that at low temper- 

 atures (57°-59°) dry air is pleasanter than 

 moist ; between 75° and 84° dry air seems 

 cooler than moist when the change is made 

 from one to the other. The last-named 

 temperatures are easily borne if the air is 

 dry. Visible perspiration was first noted 

 at 84.2° and 22% relative humidity. 

 Moist air (96% rel. humid.) made the 

 temperature of 75.2° unbearable for a long 

 time, and the experiment was possible only 

 when there was no muscular movement 

 whatever. At this temperature and humid- 

 ity there was no considerable perspiration, 

 although thirst was felt. Eespiration de- 

 creased in dry air and increased in moist 

 air. These experiments are interesting, 

 but they do not give us the actual condi- 

 tions that prevail in the outside air, as 

 usually experienced by the human body. 

 The movement of the air, which is a very 

 important factor in its effects on the sen- 

 sible temperature, and the varying amounts 

 of heat lost by conduction, radiation and 

 evaporation, according to the temperature 

 and proximity of surrounding objects, are 

 controls which do not come into play in the 

 laboratory. 



ELECTEIC SEARCH LIGHTS AS WEATHER 

 SIGNALS. 



The Monthly Weather Review for February 

 contains a note on the use of electric search 



