Chemical Agents on the Nervous System. 267 



This phenomenon is induced by so slight a Voltaic force, 

 that the limb so prepared is used as a galvanoseope. The 

 effect, however, is extremely augmented, if after making the 

 contact, a connection be made by means of a platinum wire, 

 between the points a and b, c and 6, or even between e or/ 

 and g, or "between i andy and k, g and k being entirely out of 

 the ordinary circuit. 



But these experiments involve too many questions as to 

 the effects of the electrogenic state, of reversed current, and 

 new circuits, — to be now detailed, and will, with others con- 

 nected with them, form the subject of a subsequent paper. 



I have only to add my best thanks to Dr Faraday for .the 

 kindness with which he has twice devoted an evening to 

 witnessing some of these experiments. 



[Section II., or conclusion, in our next Number.) 



On the Comparative Value of different Kinds of Coal for the 

 purpose of Illumination ; and on Methods not hitherto prac- 

 tised for ascertaining the Value of the Gases they afford. 

 By Andrew Fyfe, M.D., F.R.S.E., F.R.S.S.A., Profes- 

 sor of Chemistry, King's College University, Aberdeen, 

 &c. Communicated by the Royal Scottish Society of 

 Arts. 



[Continued from No. Ixxxix., p. 49.) 



In the preceding part of this paper, I have shewn that gases 

 from different coals not only require different times for the 

 consumpt of equal volumes, but that for these consumpts dif- 

 ferent pressures are necessary. It is of importance, there- 

 fore, to ascertain whether the consumpt and the pressure 

 bear the same ratio to each other, when different gases are 

 used, that they do when the same gas is employed. The con- 

 sumpt of gases, in some of the towns in England that I have 

 visited, along with the pressure, was as follows, — the gases 

 having been consumed from the same burner, and with the 

 same height of flame : — 



