246 Mr. J. E. Petavel. On the Heat dissipated 



surface as the perpendicular on the tangent plane. In particular, if, in 

 accordance with Mr. Allen's experiments,* there be possible forms of 

 final uniform motion for a sphere in which the resistance varies as 

 $d or u 2 (it being the velocity), it was shown that the solution would 

 still be of the form of (32) and (33), provided the distribution of the 

 viscous resistance happens to remain unchanged. 



It was pointed out that in an isotropic solid, free of cavities, at rest 

 in a liquid, the stresses are everywhere the same as if each element 

 were separately subjected to the pressure answering to its depth ; but 

 that when cavities exist in the solid the state of matters is altered; As 

 an example, a complete solution was given for a hollow spherical shell 

 fully immersed. 



It was shown that, in a completely solid body, the greatest strain 

 and maximum stress-difference theories agreed in indicating no ten- 

 dency to rupture, but that when cavities existed, it was otherwise ; in 

 particular, that in the spherical shell there is on either theory a 

 tendency to rupture, greatest at the lowest point, which approximately 

 in a thin shell varies directly as the depth and inversely as the thick- 

 ness of the shell. 



" On the Heat dissipated by a Platinum Surface at High Tempera- 

 tures. Part IV.f — High-pressure Gases." By J. E. Petavel, 

 A.M.I.C.E., A.M.I.E.E., John Harling Fellow of Owens 

 College, Manchester. Communicated by Professor Schuster, 

 F.RS. Eeceived February 7,—Kead March 7, 1901. 



(Abstract.) 



The rate of cooling of a hot body in gases at pressures up to one 

 atmosphere has received considerable attention, but with regard to 

 gases at high pressures practically no data were up to the present 

 available. It was thought therefore that an experimental investigation 

 of the subject might prove of some interest. 



The experiments were carried out with a horizontal cylindrical 

 radiator contained in a strong steel enclosure, the enclosure being 

 maintained at about 18° C. by a water circulation. 



It is shown that the rate at which heat is dissipated by the radiator 

 may be expressed by the following formula — 



E = ap* + bp? S, 



where E = emissivity in C.G.S. units = total amount of heat dissi- 



* ' Pliil. Mag.,' September and November, 1900. 



f For Parts I, II and III see ' Phil., Trans., 5 A, vol. 191, p. 501, 1898. 



