6o4 



NATURE 



[February 5, 1920 



detailed tracings packed in the ship's hold were 

 lost. Mr. Hussey's discussion shows that 

 "January 1915 was dull and overcast, only 7 per 

 cent, of the observations recording a clear blue 

 sky, 71 per cent, being completely overcast." The 

 clearest weather occurred in winter, when the sky 

 was cloudless for nearly half the time. Some in- 

 teresting results are likely to accrue when the 

 meteorological records are worked up in detail 

 and co-ordinated with other observations from 

 South Atlantic and South American stations. 

 "Temperatures on the whole were fairly high, 

 though a sudden unexpected drop in February, 

 after a series of heavy north-easterly gales, caused 

 the ship to be frozen in, and effectually put an end 

 to any hopes of landing that year. The lowest 

 temperature experienced was in July, when 35° 

 Fahr., i.e. 67° below freezing, was reached." 



For determining the position in drifting pack 

 ice, Mr. James found the theodolite a more gener- 

 ally useful instrument than the sextant, as the ice- 

 floes were found quite steady in really thick pack 

 ice, and the theodolite can be set up and levelled 

 as well as on dry land. Mr. James shows that "the 

 Endurance was carried by the ice-drift well to the 

 west of the Weddell Sea, towards the position of 

 the supposed Morrell Land, so that the accurate 

 determination of longitude became a matter of 

 moment in view of the controversy as to the exist- 

 ence of this land." The existence or non-existence 

 of Morrell Land, however, has yet to be investi- 

 gated more thoroughly, in spite of the assurance 

 of Sir Ernest Shackleton and others that it does 

 not exist. If it is a low "cluster of islands," it 

 would not have been seen at all ; the party may 

 have drifted on the floe to the west of it. 



Sir Ernest Shackleton 's appendix on the lists 

 of provisions and gear in the McMurdo Sound 

 huts is most useful and important for future ex- 

 peditions. 



Finally, the drift party reached Elephant Island, 

 which was one of the places the Admiralty had 

 planned to search. But several landings were 

 made there a century ago, and Sir Ernest Shackle- 

 ton's expedition is not the first to land there, as 

 he quite excusably supposes. The voyage to 

 South Georgia was a wonderful piece of seaman- 

 ship and endurance, and Sir Ernest Shackleton 

 has again shown that he can lead men. The story 

 of the Aurora with Macintosh and Stenhouse is 

 another^ disaster. Spencer Smith unfortunately 

 died while doing land work, which included, how- 

 ever, successful depot laying, under Macintosh. 

 The absence of scurvy, on the Weddell Sea side, 

 shows what is possible if fresh meat is mainly 

 adhered to. 



Macintosh and Hayward lost their lives in a 

 blizzard while attempting to cross from Hut Point 

 to Cape Evans on thin ice, and were blown out 

 to sea. 



Capt. Stenhouse, of the Aurora, handled that 

 vessel with marked ability during her ten months' 

 drift beset in the ice. No mention is made of any 

 systematic scientific work having been accom- 

 plished by the Ross Sea party. W. S. B. 

 NO. 2623, VOL. 104] 



TELEPHONING BY LIGHT. 



T^ELEPHONY by means of light is a particular 

 •»■ case of wireless telephony. It differs from 

 what is generally understood as wireless tele- 

 phony in no essential respect. In both cases 

 electromagnetic waves are used, but whereas in 

 ordinary wireless the waves are very long, in the 

 case of light they are very short. As a conse- 

 quence, telephony by light is easily directed by 

 means of lenses or mirrors, and constitutes a 

 secret means of communication — a state of affairs 

 not yet attained in what is popularly known as 

 Marconi wireless transmission. At the same time, 

 the use of light imposes definite limits on the pos- 

 sible range of light telephony. An uninterrupted 

 straight line is essential between the sending and 

 receiving stations, and the extreme range is there- 

 fore determined by the curvature of the earth and 

 the altitudes of the stations. 



The transmission of speech by light is rendered 

 possible by the well-known property possessed bv 

 selenium (and certain other substances) of chang- 

 ing its electrical conductivity when subjected to 

 varying illumination. Selenium thus acts as a 

 sort of electric valve controlled by light. It is 

 capable of responding to some extent to light 



■from tronsmttttf,. 



Fig 1, 



fluctuations of comparatively high frequency. If 

 a selenium cell is connected in simple circuit with 

 a battery and a telephone receiver — as shown in 

 Fig. I — fluctuating currents are obtained possess- 

 ing the same characteristics as the variations of 

 the incident light, and if the latter are of audible 

 frequency the corresponding sounds are heard in 

 the receiver. The problem of light telephony is 

 thus reduced to the production of a beam of light 

 fluctuating in intensity in accordance with the' 

 vibrations constituting the speech sounds. 



The construction of the first transmitter of this 

 kind was due to Graham Bell, who in 1880 suc- 

 ceeded in transmitting speech by means of a beam 

 of sunlight over a distance of about 200 vards. 

 Telephony by light is, indeed, almost as old as 

 ordinary telephony, and Graham Bell was the in- 

 ventor of both. It is difficult to account for the J 

 difference in the rate of development of the two * 

 systems ; the fact remains that ordinary telephonv 

 is now in common use, whilst telephony by light 

 is still a novelty. Graham Bell's first photophone 

 — as it was called — consisted of a large diaphragm, 

 silvered so as to become a mirror. Upon this 

 mirror a beam of light was projected and thence 

 reflected to the distant selenium receiver. Speech 

 sounds, falling on the diaphragm, set it in vibra- 



