It will appear, by inspection of the duties registered in the preceding ta- 

 ble, that the augmentation of the efficiency of the engines has not been the 

 effect of any great or sudden improvement, but has rather resulted from the 

 combination of a great number of small improvements in the details of the 

 operation of these machines. In these improvements more is due to the suc- 

 cessful application of practical experience than to any new principles de- 

 veloped by scientific research. Mr. John Taylor, in his " Records of 

 Mining," has traced the successive improvements on which the increased 

 duty of engines depends, and has connected these improvements with their 

 causes in the order of their dates. The following results, abridged from his 

 estimates, may not be uninteresting : — 



In 1769, soon after the date of the earliest discoveries of Mr. Watt, but 

 before they had come into practical application, Smeaton computed that the 

 average duty of fifteen atmospheric engines, working at Newcastle-on-Tyne, 

 was 5,590,000. The duty of the best of these engines was 7,440,000, and 

 that of the worst 3,220,000. 



In 1772, Smeaton commenced his improvements on the atmospheric engine, 

 and raised the duty to 9,450,000. 



In 1776, Watt obtained a duty of 21,600,000. 



At this time Smeaton acknowledged that Watt's engines gave a duty amount- 

 ing to double that of his own. 



In 1778-79, Watt reported a duty of 23,400,000. 



From 1779 to 1788, Watt introduced the application of expansion, and raised 

 the duty to 26,600,000. 



In 1798, an engine by Boulton and Watt, erected at Herland, was reported 

 as giving a duty of 27,000,000. 



This engine, which was probably the best which at that time had ever 



