Chemistry and Physios. 481 



solar heat accompanied by small annual rainfall, of luxuriant 

 vegetation, and of large water power are specially instructive. 

 The volume ends with " References," " Bibliography," and a 

 subject index. h. s. u. 



12. Effect on the Propagation of Electric Waves of the Total 

 Eclipse of the Sun, 21st August, 191Jf.. — A committee of the 

 British Association for the Advancement of Science has recently 

 issued the following circular: 



" The forthcoming total eclipse of the sun affords an exceptional 

 and important opportunity of adding to existing knowledge of 

 the propagation of electric waves through air in sunlight and 

 in darkness, and across the boundaries of illuminated and 

 unilluminated regions. The eclipse will be total along a strip 

 extending from Greenland across Norway, Sweden, Russia and 

 Persia to the mouths of the Indus. In Russia the dm-ation of 

 totality will be a little more than two minutes. 



"There are two main points calling for investigation during the 

 eclipse. In the first place, the propagation of signal-bearing 

 waves through air in the umbra and penumbra will probably 

 obey laws different as regards absorption and refraction from 

 those obeyed in illuminated air. In the second place, the 

 strength, frequency and character of natural electric waves, and 

 of atmospheric discharges, may vary. The variations may occur 

 either because the propagation of natural waves from distant 

 sources is facilitated or impeded by the eclipse, or, possibly, 

 because the production of natural electric waves or atmospheric 

 discharges is for some unknown reason affected by the eclipse. 

 These points have previously been investigated to only a slight 

 extent. The observers of signals during the solar eclipse of 17th 

 April, 1912, nearly all agreed that the strength of the signals 

 was greater during the eclipse than an hour before or after. 

 There was only one special observation of strays during the same 

 eclipse, when very pronounced and remarkable variations were 

 recorded during the passage of the shadow-cone across Europe. 



" To investigate the propagation of signals across the umbra it 

 will be necessary to arrange for wireless telegraph stations on 

 either side of the central line of the eclipse to transmit signals 

 at intervals while the umbra passes between them. This 

 transit of the umbra occupies about two minutes. It is thus very 

 desirable that the Scandinavian and Russian stations should 

 transmit frequently throughout several times before, during, and 

 after totality. But stations other than those favoured by their 

 proximity to the central line should endeavor to keep a complete 

 record of the variations of signals during the eclipse. Stations 

 in Europe west of the central line and stations in the Mediter- 

 ranean and in Asia Minor may find noticeable changes in the 

 strength of signals, particularly long distance signals, between 

 the hours of 10 a. m. and 3 p. m., Greenwich time ; and it is 

 probable that the stations of India and East Africa, and ships in 

 the Indian Ocean, may feel the effect of the penumbra in the 

 afternoon. On the other hand, ships in the Atlantic, and fixed 



