3 8 HER OES OF INVENTION AND DISCO VER Y. 



the water into its interior, that it might be difficult in that case 

 to convey it away as fast as it would accumulate. But he found 

 that the condensation was not effected in this manner with so 

 much rapidity as was desirable. It was necessary for him, too, 

 at any rate to employ a pump attached to the condenser, in 

 order to draw off both the small quantity of water deposited 

 by the cooled steam, and the air unavoidably introduced by 

 the same element — either of which, if allowed to accumulate, 

 would have impaired the perfect vacuum necessary to attract 

 the steam from the cylinder. He therefore deiermined event- 

 ually to admit also the additional quantity of water required for 

 the business of condensation, and merely to employ a larger 

 and more powerful pump to carry off the whole. 



Such, then, was the remedy by which the geniu:J of this great 

 inventor effectually cured the first and most serious defect of 

 the old apparatus. In carrying his ideas into execution, he 

 encountered, as was to be expected, many difficulties arising 

 principally from the impossibility of realising theoretical perfec- 

 tion of structure with such materials as human art is obliged to 

 work with ; but his ingenuity and perseverance overcame every 

 obstacle. One of the things which cost him the greatest trouble 

 was, how to fit the piston so exactly to the cylinder is without 

 affecting the freedom of its motion, to prevent llie passage of 

 the air between the two. In the old engine this end had been 

 attained by covering the piston with a small quantity of water, 

 the dripping down of which into the space below, where it 

 merely mixed with the stream introduced to effect the conden- 

 sation, was of little or no consequejice. But in the new 

 construction, the superiority of which consisted in keeping this 

 receptacle for the steam always both hot and dry, such an 

 effusion of moisture, although only in very small quantities, 



