the Frussian Coal-Mineg. 193 



neither inflammable gases nor empyreumatic oils make their 

 appearance. Whether both presented themselves in earlier 

 times, is not known to me. Subterranean conflagrations, 

 without the evolution of inflammable gases, can hardly be 

 imaguied ; for the heat produced by a portion of a burning 

 stratum will cause another portion of the same stratum to be 

 exposed to a dry distillation. But the liquid products of this 

 distillation, especially if the process occurs at some depth, can 

 be taken up by the nearest beds ; such as beds of sandstone or 

 slate-clay, nay even of coal itself, which has not been reached 

 by the fire ; and it can be accumulated in them in the form 

 of bitumen. 



Description of a Folyphotal Lamp, and Beflector of Single Cur- 

 vature, employed in Steam-vessels, Canal-boats, SjC. By 

 John Scott Russell, A.M., F. R. S. E., V. P. S. A.* 

 (Communicated by the Society of Arts.) 

 Several years ago, I was applied to by Mr Ellis, the Secre- 

 tary of the Union Canal, to assist in some contrivances for ex- 

 pediting canal transport, and adding to its security. Amongst 

 other things, this lamp and reflector resulted from this appli- 

 cation. It has been in constant use ever since ; it is now used 

 also on the Forth and Clyde Canal, and is about to be intro- 

 duced in steam- vessels. It is also capable of being used with 

 advantage in many other situations, where concentration is 

 not required. 



The view with which this lamp was constructed v/as that 

 of throwing light forward before the boat upon all the objects 

 in a certain range, and to a great distance, so as to illuminate 

 the banks of the canal, to throw light upon any vessel coming 

 in the opposite direction,— to throw a light on the horse's path 

 and on the arches of the bridges, so that the horses, their 

 rider, and the helmsman, might clearly see and avoid them. 

 All this the lamp has, for four or five years, been successfully 

 accomplishing. It is, besides, not expensive, and is kept in 

 order by the common boatmen without difficulty. 



* Head before the Society of Arts for Scotland, November 13. 1839. 

 VOL. XXVIII. NO. LV. JANUARY 1840, N 



