PBESIDENT'S ADDRESS. 15 



increase of temperature. Though diamonds, with the ex- 

 ception of exceedingly small ones, cannot be made artificially, 

 yet both rubies and sapphires are produced by melting up 

 small cuttings and bits of real stones, or by melting colourless 

 corundum with a colouring matter. The difference between 

 the natural and artificial gems can be seen by examining any 

 small air bubbles, &c., present, which in the natural stones 

 follow in shape and position the planes of crystallisation. 



ENGINEERING. 



No one having yet invented a means of passing freely and 

 making long excursions through the water or the earth, the 

 conquest of the air remains for the present the most exciting 

 engineering novelty, and fresh records are continually made 

 as flying machines are improved and aviators gain experience. 

 Aeroplanes have now been actually used in warfare and have 

 shewn that they can act without very great danger to them- 

 selves, and drop bombs amongst the enemy as well as recon- 

 noitre their position, yet so far they do not seem in either of 

 these points to have actually been of very important service. 

 A postal service was instituted but soon abandoned, but the 

 longer distances covered in various race competitions shew 

 that the science is developing. Experiments have been made 

 with a gliding machine, without power, which with a strong 

 wind has enabled the aviator to support himself in a stationary 

 position in the air for more than five minutes. The large air- 

 ships \vhich have been tried are cumbersome and very liable 

 to disaster, and do not appear to increase in reliability to 

 the same extent as the aeroplanes. Amongst the subjects 

 which occupied the engineering section of the British Associa- 

 tion were the rolling of ships, their electrical steering and 

 propulsion, and the gyro-compass, consisting of a gyroscope 

 running in a mercury bath at 20,000 revolutions a minute. 

 Owing to the difficulties of preventing disturbances of a 

 magnetic compass through the large quantity of iron in a 



