130 Mr. Willis on the Pressure of a 



phenomenon vnHh respect to the escape of steam under high 

 pressure, and the danger of failure to which the common safety- 

 valves of steam-boilers were exposed, by this singular factv 

 M . Hachette then succeeded in simplifying the form of the ex- 

 periment, so that it might be performed by a pair of com.mon 

 bellows, or a stream of air from the mouth. He also produced 

 the same effects by using a stream of water instead of air. (The 

 particulars may be found. Bull. Univ. E. vii. pp. 41. 104. Ann. 

 dc Chimie, 1827, T. XXXV. p. 34, and T. XXXVI. p. 69. Quarterly 

 Journal, 1827, Vol. I. p. 472, and Vol. II. p. 193. Some similar 

 phenomena may, however, be seen in Young's Nat. Phil. Vol. I. 

 pp. 298, 778.) 



My object in the present Memoir is to detail some experiments 

 which were undertaken for the purpose of examining some of 

 the laws of this phenomenon more minutely than has hitherto 

 been done. 



In order to put it into a shape more convenient for investi- 

 gation, some tubes of different diameters, terminating in flat 

 plates, were connected to the wind-chest of an organ capable of 

 furnishing a regular blast of any pressure not exceeding six 

 inches of water, and a balance of light wood about six feet 

 long, together with a number of discs of tin of various diameters, 

 which could be attached by means of a screw to one of its ex- 

 tremities, being provided ; then, by adding weights to the other 

 extremity, and counterbalancing these by placing known weights 

 on the centers of the discs, the effects of varying the orifice, 

 pressure, &c. could be measured. The balance was made of 

 considerable length, that the parallelism of the discs might not 

 be sensibly affected by its motion. 



Let CBD, Fig. 1, be a section of the lower plate provided 

 with its tube AB, through which a constant blast is maintained. 

 Bring the upper disc GH gradually down to CD, preserving its 



