166 



Sir W. Siemens. 



[Apr. 26 r 



endosperms, and in the prosenchymatons bast fibres, bnt is of much 

 wider if not of universal occurrence. At any rate we were now in a 

 position to get a clearer insight into such phenomena as the downward 

 movement of a sensitive leaf upon stimulation, of the wonderful 

 action of a germinating embryo on the endosperm cells, even on those 

 which are most remote from it, of the action of a tendril towards it& 

 support, and of a series of phenomena in connexion with general cell 

 mechanism, which were too numerous to mention, and could not be 

 treated of in his present paper. 



The paper is accompanied by forty figures, which illustrate the 

 principal instances of protoplasmic continuity referred to in the 

 text. 



IV. " On the Dependence of Kadiation on Temperature." By 

 Sir William Siemens, F.E.S., D.C.L., LL.D. Keceived 

 April 25, 1883. 



Sir Isaac Newton held that the radiation of heat from a hot body 

 increased in arithmetical ratio with the difference of temperature 

 between it and the surrounding bodies. This law forms a rough 

 approximation to the truth over a very limited range of temperature. 

 MM. Dulong and Petit carried out an elaborate experimental 

 research on the rate of cooling of hot bodies by radiation, extending 

 to somewhat higher temperatures, and deduced from their observa- 

 tions the empirical formula — 



Sate of cooling =m(V0077y(V0077 T - t -l). 



Here T is the temperature of the hot body in degrees Centigrade, t 

 the temperature of the surrounding matter, and m is a constant 

 depending on the nature o! the radiating body. This formula agrees 

 very fairly with experimental results for ordinary temperatures, but r 

 like Newton's law, it has been shown that it cannot be applied for a 

 wider range. 



The anomalous results which Newton's law and the formula of 

 MM. Dulong and Petit lead to, when applied to the cooling of 

 bodies at a very high temperature, are well illustrated by the 

 attempts at deducing therefrom the temperature of the solar photo- 

 sphere. Waterston and Pere Secchi (in his work entitled " Le Soleil "),. 

 following Newton's hypothesis, obtained 10,000,000° C. as the prob- 

 able solar temperature, and Captain J. Ericsson, on the same hypo- 

 thesis but assuming other constants, arrived at a temperature between? 

 2,000,000° and 4,000,000° C. Strangely contrasting with these 

 determinations are those of Pouillet in 1836, and Vicaire -in 1872,. 



