474 Miscellaneous Intelligence, 



thrpuiyliout a space sqfficiently large to permit the pressure of the 

 {^tmosphere to be stronger than that of the vapour. ]\I. Clement 

 ]\s^^ flemonstrated by several experiments that this partial vacuum 

 ]feaHy exists in the space which serves as an issue for the vapour, just 

 as pcpurs in tjie PQiiical tubes which are applied to orifices through 

 which liquids are flpwing. He has shown, that the interval which 

 ^epara^eg. thp t\\Q plates between which the vapour escapes is a 

 tr\ie cpnoidp. In fact, this interval is formed of conceptric rings, of 

 ^Y^iipl^ the surface augments in proportion to the diameters ; andy 

 consequently, the elastic fluid as it passes from the smaller to the 

 l^rg^r ring has successively filled the spaces in which it has 

 assumed a decreasing density, until beneath that which corresponds 

 to atmospheric pressure, and this in consequence pf the active 

 force wjth wl^ich ^ach molecule is animated when it escapes firom 

 its ^rst pr^ssurt^. 



M. Clement finds that the theory which Daniel Bernouilli has 

 given for the effect of conical or cylindrical jets applies perfectly to 

 these curious phenomena with vapour, so that the effects were 

 explained, as it were, before they were observed. The great degree 

 of cold produced by compressed vapour at the moment of its ex- 

 pansion in the air, is also an effect of the active force which it 

 possesses at the moment of its issuing forth, which enables it to 

 acquire a very low tension. The jet is then formed of vapour, of 

 the fprpe pf one-half or one-fourth of an atmosphere, and which 

 consequently possesses only the corresporiding temperature, i.e. 60 

 or 50 degrees C. This temperature is still further reduced by the 

 quantity of air which the vacuum draws to it, and thus a wind 

 rather cold than hot is occasioned. 



M. Clement proposes some alterations in safety-valves, and con- 

 siders the addition of a weak tube to steam-boilers as a perfect 

 security. He recommends it to be of considerable diameter, and 

 capable of supplying when burst a large vent for the vapour, so as 

 to be sufficient to allow of the sudden productions of vapour which 

 sometimes take place, and to which probably numerous accidents 

 are due. — E. vii. p. 104. 



5. Transference of Meat hy change gf capacity in Gas. — Many 

 of the copper vessels in wl^ich gas is compressed at the Portable 

 Gas-works are cyhnders, from two to three feet in length, termi- 

 nated by hemispherical ends. These are attached at one end to 

 the system of pipes by which the gas is thrown in, and being so 

 fixed, the communication is opened ; it frequently happens, that 

 g^S previously at the pressure of thirty atmospheres in the pipes 

 ari^ attached recipients, is suddenly allowed to enter these long 

 ^as-yessels, at which time a curious effect is observed. That end 

 of the cylinder at >yhich the gas enters becomes very much cooled, 

 whilst, on the contrary, the other end acquires a considerable rise 

 pf tempexat\^r^. This effect is produced by change of capacity in 



