Mr. Perkins's Steam-Engine. 315 



following ingenious contrivance. It should be remembered, 

 that owing to the small extent of surface exposed to the ex- 

 pansive force of the steamy and tlie latter being generated only 

 in sufficient quantity for each succeeding stroke of the piston, 

 there is much less liability to accident from this engine than in 

 most other high-pressure engines. To prevent, however, the 

 possibility of such an event, the induction pipe, in which the 

 steam is produced, is calculated to withstand an internal force 

 of 4000 pounds to the square inch, and it is also provided with 

 a thin copper tube, which is calculated to burst at a pressure of 

 1000 pounds; while the pressure under which Mr. P. woi'ks 

 the engine does not exceed 500 pounds on the square inch. 



In order to demonstrate the perfect safety of the operation 

 of this engine, notwithstanding this immense internal pi'essure, 

 Mr. Perkins has on several occasions urged the power of the 

 steam till it bursts open the sides of the copper tube, without 

 occasioning the smallest risk either to the spectator or to any 

 other part of the apparatus. This mode of allowing the escape 

 of the steam by rending open the sides of the ball, (which is 

 made of a determinate strength,) is probably superior in the 

 certainty of its operation to any modification of safety valves. 



It is also a veiy remarkable fact, that the steam which 

 escapes in this case is not by any means of that elevated tem- 

 perature which might have been expected fi'om its prodigious 

 expansive force*. This fact seems to in\olve some points con- 

 nected with the doctrine of latent heat, or the conversion of 

 fluid into gaseous matter, and vice versa, with which we are 

 at present but very imperfectly acquahited. We understand 

 Mr. P. is further engaged on some very important inquiries 

 on this most intricate branch of natural philosophy. 



We have not heard any comparative estimate of the price 

 of Mr. P.'s engines, but we apprehend their original cost will 

 be very considerably lower than that of others; while they can 

 be worked with 1-1 0th part of the fuel, and occupy only a 

 fifth part of the space required for those of the low-pressure 

 construction. The latter point is one of the highest import- 

 ance, in situations where manufacturers are limited for room, 

 as in the metropolis and other great tow ns. 



The very superior oeconomy of these engines over all others, 

 not only in the consumption of fuel and water, but in the weight 

 of materials, must also render them peculiarly adapted for 

 locomotive engines; and we entertain little doubt that steam 

 carriages will, ere another 20 years have elapsed, become as 

 generally adopted among us as steam vessels are at the pre- 



* On the tcin|)craturc of steam at dirt'cicnt degrees of compression, sec 

 Mr. I'hili|) Tjivlor's pjipcr, p. 4.i2, vol. Ix. 



U r 2 sent. 



