14 PRESIDENT'S ADDRESS. 



much interest during the war, but the transmission of the 

 sound was generally looked upon as taking place through the 

 air. It has however been found that these sounds are trans- 

 mitted very clearly through the earth and often audible in 

 gravel pits or other excavations, or by putting the ear to the 

 ground, when they cannot otherwise be heard. 



ELECTRICITY. 



At the annual visitation of Greenwich observatory at which 

 many astronomers and others were present, on June 5th last, 

 it was stated that the mean magnetic declination for 1919 was 

 14 18-2' and that it is decreasing about 9.6' annually so that 

 it should reach zero about the end of the century. One of the 

 most remarkable inventions in connection with wireless tele- 

 graphy is that of a machine which automatically prints off the 

 message received in ordinary type. A perforated strip in the 

 Morse code is first produced which is used as a guide for the 

 printing of the letters in ordinary type. By means of a 

 telephone receiver with a trumpet attachment, wireless mess- 

 ages can be heard by a large audience, and developments in 

 wireless telephony continue. Arrangements have been made 

 for the diffusion of astronomical information from Nauen in 

 Denmark, so that cases in which immediate observation is 

 desired in different countries, may not be delayed. Longitude 

 can be also very accurately determined in this way, as at 

 Adelaide, Australia, where signals from Lyons can be received, 

 and where the accepted longitude has been slightly corrected 

 by these means. A valuable recent invention for navigating 

 purposes is a submarine cable laid in the track along which a 

 ship has to pass in entering a harbour. An alternating 

 current is sent through the cable, and wire coils are placed on 

 each side of the ship and connected with two telephones on 

 the bridge. When the sounds in each telephone are of equal 

 intensity the ship is over the cable, and if they become unequal 

 the course can be adjusted until equality is restored. A cable 

 of this sort has been laid at Portsmouth, with satisfactory 

 results. Experiments have been carried out to a depth of 30 

 fathoms, but it will probably be effective at greater depths. 



