48 CONTEMPORARY SCIENCE 



application under peace conditions as aids to navigation 

 I may mention directional wireless, by which ships and 

 aircraft can be given their positions and directed. 



Leader gear, first used by the Germans to direct their 

 ships through their minefields, and subsequently used by 

 the Allies, consists of an insulated cable laid on the bot- 

 tom of the sea, earthed at the farther end, and through 

 which an alternating current is passed. By means of 

 delicate devices installed on a ship, she is able to follow 

 the cable at any speed with as much precision as a rail- 

 less electric 'bus can follow its trolley wire. Cables up 

 to 50 miles long have been used, and this device prom- 

 ises to be invaluable to ships navigating narrow and tor- 

 tuous channels and entering or leaving harbors in a 

 fog. 



Aircraft. It may be justly said that the development in 

 aircraft design and manufacture is one of the astonishing 

 engineering feats of the war. In August, 1914, the Brit- 

 ish Air Service possessed a total of 272 machines, 

 whereas in October, 1918, just prior to the Armistice, the 

 Royal Air Force possessed over 22,000 effective machines. 

 During the first twelve months of the war the average 

 monthly delivery of aeroplanes to our Flying Service was 

 fifty, while during the last twelve months of the war the 

 average deliveries were 2.700 per month. So far as aero- 

 engines are concerned, our position in 1914 was by no 

 means satisfactory. We depended for a large proportion 

 of our supplies on other countries. In the Aerial Derby 

 of 1913, of the eleven machines that started, not one had 

 a British engine. By the end of the war, however, British 

 aero-engines had gained the foremost place in design and 

 manufacture, and were well up to requirements as regards 

 supply. The total horse-power produced in the last twelve 

 months of the war approximated to eight millions of brake 

 horse-power, a figure quite comparable with the total 

 horse-power of the marine engine output of the country. 



In view of the recent trans-Atlantic flights, I feel that 



