162 Foreign Literature and Science. 



like artificial fire works, and presses against the disk more 

 than before, not only is the disk not driven away, but it ad- 

 heres to the plate even when the jet is directed downwards. 

 It remains suspended in opposition to its gravity, and can be 

 detached only by force. The same result takes place, in an 

 experiment with the wind which issues from the large bellows 

 of a furnace. 



Another fact, also curious, though already well known, is, 

 that a current of steam from a boiler in which it is very hot 

 and much compressed, seems like a cool wind compared with 

 a current at one half the temperature and at one twentieth 

 of the pressure. 



From his first experiments, M. Clement concludes that 

 common safety valves, which consist of real disks placed up- 

 on openings in flat plates, present a danger, inherent in their 

 form. Scarcely are they raised, so as to allow a thin plate of 

 steam to escape, before it becomes impossible for them to rise 

 higher, and if the production of vapour is too considerable for 

 the small opening which may have obtained, and for the 

 strength of the boiler, an explosion may take place, though 

 the safety valve is open. This is in fact what sometimes 

 happens, and which has hitherto appeared incredible. M. 

 Clement had not time to give a full explanation of these sin- 

 gular phenomena. We only know that he attributes them 

 to the vacuum which takes place in the current of steam, in 

 consequence of the extreme swiftness of its particles, and of 

 the conical form the current assumes between the adjacent 

 plates. The current, from its great force is so expanded to- 

 wards the borders, as to become much less than the pressure 

 of the atmosphere, which acts upon the moveable disk forci- 

 bly enough to resist the vapour. 



The remedy for this danger is a good proportionate space 

 between the orifice and their borders. The first should be 

 large and the others small. Besides, the addition of a coni- 

 cal tube to the safety valve, would diminish the effect of at- 

 mospheric pressure, and of the weight with which they are 

 loaded. M. Clement thinks that experiment alone can de- 

 termine what is the best modification of safety valves to re- 

 move the danger he points out, and which has been so long 

 unnoticed. He wishes the manufacturers to make the neces- 

 sary trials, agreeably to the theory which he has given. 



Idem. 



