PRESIDENT'S ADDRESS. 13 



and granting certificates of competency. Analyses of the 

 ashes of a number of different plants have shewn the presence 

 in the plants of minute quantities of some of the rare elements, 

 such as lithium, rubidium, caesium, chromium, vanadium, 

 barium, strontium, and titanium. Aluminium, lithium, and 

 rubidium were practically always present. In these experi- 

 ments the earth in which the plants were grown contained 

 traces of the elements found in them. As regards the pro- 

 duction of nitric acid, ammonia, and other useful chemicals 

 from waste products, some progress has been made, as well 

 as in the fixation of the nitrogen contained in the air, though 

 this latter has not yet taken a practical form in this country. 

 Some substitutes for platinum, which has now reached a value 

 of about five times that of gold, have been discovered and can 

 be used for certain purposes. They are mostly compounds 

 of gold with iridium, titanium, or other metals. 



ENGINEERING. 



The Report of the Advisory Committee for Aeronautics 

 for the year 1916-7 has lately been issued, and deals with 

 much experimental work that has been carried out with 

 regard to aeroplanes both in their structure and materials, 

 and in their behaviour in flight. One great difficulty is that 

 of finding the course when the earth is hidden by clouds, 

 as the aviator is unable to perceive the effect of the wind which 

 carries him out of his direct line. Our aeroplanes seem 

 to have improved very much of late and to have quite the 

 upper hand of the German ones, from the relative numbers 

 of those destroyed which are published in the newspaper 

 reports. A flight of 650 miles, from Turin to London, was 

 made on September 24th last, the journey occupying 7 hours 

 20 minutes, a rate of 89 miles per hour. The same aviator 

 had previously made a flight of 920 miles without stopping, 

 from Turin to Naples and back, a fine record. The use of 

 aeroplanes for postage and commercial purposes after the 

 war is being considered, and it has been calculated that 



