40 THE HISTORY OF [SECT. i. 



effective power of engines. But the complexity and expense of apparatus to 

 obtain so small an increase of power, renders this and some other expedients of 

 that time of little if any value. 



1801. JOSEPH BRAMAH ; born 1749, died 1814. 



52. The rotary engine, the joint product of Messrs. Bramah and Dickinson, 

 has already been noticed. (Art. 39.) In 1801 Mr. Bramah obtained a patent for 

 a new mode of applying the four-passaged cock to steam engines, with some other 

 variations in their construction. 



The four-passaged cock he made to turn continually in the same direction, and 

 yet produce the same effect as by turning it backwards and forwards ; but by turn- 

 ing constantly the same way, the wear is rendered more equable, and consequently 

 the combination is more durable. 



He also adjusted the movements so as to give, at the proper time, as instantaneous 

 and free a passage to the cylinder and condenser as possible ; and formed the 

 apertures so that the cone might be pressed equally into its seat by the force of 

 the steam. 



53. A series of tables for the proportions of the cylinders of atmospheric 

 engines, to produce a given effect, were published in 1801 by Mr. Thomas Fen- 

 wick, whose employment in the management of coal works near Newcastle gave 

 him a good opportunity of knowing what would answer best in practice. 



He infers from some experiments, that the whole friction of the atmospheric 

 engine is about four pounds per square inch, on the area of the piston ; and on 

 account of the frequent bad effects attending designing an engine with too small 

 an allowance for excess above its ordinary work, he makes his computations at 

 five pounds and a half effective power for each square inch of piston. 



In a later edition of his work he gives tables for an improved atmospheric engine 

 with a separate condenser, in which the ratio of the effect is as 17 : 10, when the 

 same sized cylinder is used. The saving of fuel he does not mention, as at coal 

 works it is not considered of much importance ; for if the first expense of an engine 

 be small, and its operation simple and efficient, it is of more value to a coal owner 

 than a finer piece of machinery. 



1801. JOHN DALTON. 



54. At this period a knowledge of the nature and properties of vapours began 

 to become important in chemical science, in meteorology, and in other branches of 

 natural philosophy ; and therefore a wholly different class of writers engaged in the 



