210 



Dr. C. W. Siemens. 



[Mar. 4 y 



The weight of the core (which may be varied), determines the force 

 of current that has to pass through the regulating coil in order to 

 keep the weight in suspension, and this in its turn is dependent upon 

 the resistance of the arc. The result is that the length of the arc is 

 regulated automatically, so as to maintain a uniform resistance 

 signifying a uniform development of light. 



III. " On the Influence of Electric Light upon Vegetation, and 

 on certain Physical Principles involved." By C. William 

 Siemens, D.C.L., LL.D., F.R.S. Received March 1, 1880. 



Although according to Ste. Claire Deville the dissociation of C0. 2 

 and H 2 at atmospheric pressure commences at a temperature not 

 exceeding 1,200° C, the reverse action, namely, combustion, continues 

 to be sufficiently active to increase the heat of a flame until a tempera- 

 ture of probably 2,200° C. is reached, of which the Deville oxygen 

 blast and the regenerative gas-furnace furnish examples. 



In the working out of a process, by means of which steel and fused 

 iron are produced in large masses on the open hearth of the regenera- 

 tive gas-furnace, I have had frequent opportunities of observing the 

 utmost limit of temperature practically attainable by means of the 

 combustion of carbonaceous substances. The heat of that furnace is 

 not dependent upon a blast or upon chimney draught, and the pres- 

 sure within the furnace balances the external atmospheric pressure so 

 completely that the large working doors may be opened occasionally 

 for inspecting the metal. On these occasions it may frequently be 

 observed that serrated clouds of highly heated combustible gases 

 pass through the furnace chamber (as may be seen through obscured 

 or coloured glasses) without suffering apparently any diminution 

 through contact with an excess of heated oxygen, showing that the 

 limit of furnace heat, or the point of complete dissociation, has been 

 nearly reached. 



When thus brought face to face with the utmost limit of heat 

 attainable by combustion, it is surprising how slight is the incon- 

 venience (in the absence of heated matter flying about) experienced 

 in approaching the open furnace, and how much higher must be the 

 temperature of the sun or of the electric arc when the effects of 

 distant radiation suffice to break up compounds such as nitrate of 

 silver in a few seconds. Some years ago I undertook certain experi- 

 mental inquiries having for their object to study the effect of radiant 

 energy upon the ordinary products of combustion, C0 2 and H 2 0, 

 presenting them in an extremely rarefied conditon to solar and electric 



