No. 6.] PRESIDEiNT's ADDRESS B. A. A. S. 355 



boiler pressure is limited, however, by consideratioDS of safety 

 and convenience of construction, and the range of working tem- 

 perature rarely exceeds 120° C. except in the engines constructed 

 by Mr. Perkins, in which a range of 160° C, or an expansive 

 action commencing at 14 atmospheres, has been adopted with 

 considerable promise of success, as appears from an able report 

 on this engine by sir Frederick Bramwell. To obtain more 

 advantageous primary conditions we have to turn to the caloric 



or oas-engine, because in them the co-efficient of efficiency ex- 



' T— T" 

 pressed by — ^ , may be greatly increased. The value would 



reach a minimum if the initial absolute temperature T could be 

 raised to that of combustion, and T' reduced to atmospheric 

 temperature, and these maximum limits can be mnch more nearly 

 approached in the gas-engine worked by a combustible mixture 

 of air and hydrocarbons than in the steam-engine. 



Before many years have elapsed we shall find in our factories 

 and on board ships engines with a fuel consumption not exceed- 

 ing 1 pound of coal per efiective horsepower per hour, in which 

 the gas producer takes the place of the somewhat complex and 

 dangerous steam-boiler. The advent of such an engine and of 

 the dynamo-machine must mark a new era of material progress 

 at least equal to that produced by the introduction of steam 

 power in the early part of our century. 



When the British Association met at Southampton on a for- 

 mer occasion, Schonbein announced to the world his discovery of 

 gun-cotton. This discovery has led the way to many valuable 

 researches on explosives generally, in which Mr. Abel has taken 

 a leading part. 



The extraordinary difference of condition, before and after its 

 ignition, of such matter as constitutes an explosive agent, leads 

 up to the consideration of the a^o-resate state of matter under 

 other circumstances. As early as 1776 Alexander Volta ob- 

 served that the volume of glass was changed under the influence 

 of electrification, by what he termed electrical pressure. Dr. 

 Kerr, Govi, and others have followed up the same inquiry, which 

 is at present continued chiefly by Dr. George Quincke, of Heid- 

 elberg, who finds that temperature, as well as chemical constitu- 

 tion of the dielectric under examination, exercises a determining; 

 influence upon the amount and charcter of the change of volume 



