PRIME-MO VERS. 377 



tific Congress is probably not the place for a popular explanation, I 

 will venture to repeat it. The principle may be summed up in one 

 word, " concentration." The steam that issues from an orifice of an 

 area of I, when condensed, has a sectional area (according to the ori- 

 ginal pressure of the steam) of only ^th, or ^o th > or K^Q^) as the 

 case may be. Thus the velocity remaining the same, and the weight 

 the same, the energy of the steam issuing from an area of I is concen- 

 trated 200, 400, or 800 times upon the area, due to the smaller trans- 

 verse section of the liquid stream. 



This concentration of energy is far more than sufficient to enable 

 the fluid stream to re-enter the boiler from which the vaporous stream 

 started ; and so much more than sufficient, that it may be diluted by 

 taking with it a certain quantity of water which was employed in the 

 condensation of the steam, and is required for the feeding of the 

 boiler. 



With a view to obtaining economy in fuel many attempts have been 

 made to employ some other agent than steam as the means of de- 

 veloping the power latent in fuel, but it is imperative that I should 

 dismiss these with a mere enumeration. A very interesting engine of 

 this kind (because, excluding Hiero's toy and smoke jacks, it is, so 

 far as I know, the first proposition for obtaining rotary motion by 

 the aid of heat), was the fire wheel of M. Amonton, of which an 

 account is to be found in the first volume of the French Academy of 

 Sciences, date 1699. On referring to that volume I do not see 

 it is stated in terms the machine was ever put to work, although 

 it is said that M. Amonton made many experiments to convince 

 the Academy of the practicability of his invention. M. Amonton 

 proposed to have a metallic wheel revolving on a horizontal axis ; 

 the outer rim of the wheel was to be divided into a number of 

 separate air cells, each of which had a channel so as to communi- 

 cate with other cells, arranged round the wheel nearer to the centre 

 than the air cells ; the air cells as they passed over a fire were to be 

 heated, and the air was to drive the water up to one side of the wheel, 

 so as to keep that side always loaded, and thus give the wheel a ten- 

 dency to revolve. The cells, after leaving the neighbourhood of the 

 fire, were to be cooled by passing through water, to re-contract the air 

 ready for the next operation. 



