476 



Mr. W. Sutherland on Thermal 



Hour. 



0-1 A.M 



1-2 ,, 

 2-3 „ 

 3-4 „ 

 4-5 „ 

 5-6 „ 

 6-7 „ 

 7-8 „ 

 8-9 „ 

 9-10 ,-, 

 10-11 „ 

 11-12 „ 

 0-1 p.jj 

 1-2 „ 

 2-3 „ 

 3-4 „ 

 4-5 „ 

 5-6 „ 

 6-7 „ 

 7-8 „ 

 8-9 „ 

 9-10 „ 

 10-11 ,, 

 11-12 „ 



Yelletri. 



Verona. 



Vesuvius. 



58 



21 



14 



52 



15 



21 



42 



19 



23 



46 



20 



21 



34 



20 



14 



36 



24 



14 



65 



27 



16 



66 



30 



19 



96 



29 



17 



97 



59 



17 



87 



81 



35 



75 



33 



37 



83 



23 



40 



78 



29 



33 



82 



31 



47 



75 



42 



32 



68 



33 



32 



73 



23 



19 



48 



18 



13 



48 



13 



15 



51 



25 



13 



34 



33 



17 



52 



29 



13 



45 



23 



25 



Italy. 



264 

 238 

 264 



250 

 248 

 257 

 260 

 308 

 407 

 482 

 527 

 436 

 452 

 388 

 443 

 454 

 385 

 347 

 294 

 276 

 346 

 318 

 286 

 247 



XLIX. Thermal Transpiration and Radiometer Motion. 

 By William Sutheklanl *. 



[Continued from p. 391.] 

 Pakt II. — Radiometer Motion. 



T) EYNOLBS, in treating of radiometer motion in con- 

 -i-V nexion with his discovery of thermal transpiration, 

 showed that fundamentally both phenomena are traceable to 

 the same general cause : the object of the rest of this paper is 

 to bring out this fact more clearly, and to establish theoretically 

 the general laws of radiometer motion for comparison with 

 the experimental results of Crookes and Pringsheim. 

 ^In the theory of thermal transpiration, we have seen that 

 under suitable conditions the variation of temperature along 

 a passage through a porous plate can produce a certain 

 difference between the pressures at its hot and cold ends, and 

 therefore the solid wall of the passage must be exerting a 

 tangential force F from cold to hot, such that, R being the 

 mean radius of the passage, 



and, accordingly, the gas in the passage exerts a tangential 



* Communicated by the Author. 



