TRANSITION RESISTANCE -—MACGREGOR. 47 
injures its use for general purposes; it can, however, be utilized 
for colliery work, to the economy of the better coal. The coal 
from the lower portion is equal to the average of that mined in 
Pictou County. The theoretical evaporative power compares 
favorably with that of the coals from the various counties of the 
Province, as will appear from the following table: 
Pictou Co’y, average of 5 coals. Theoretical evaporative power 8°66 
Cumberland Co., “ iat S oS ae 
ape Breton “ “ 12 “ ‘ g “8:56 
Inverness on Pa ze aa OO 
The average evaporative power of the lower part of the 
seam under consideration is 847. All the evaporative powers 
are calculated by REGNAULT’S formula, for comparison with the 
admiralty coal trials, although later researches have somewhat 
altered the values determined by him. The table is taken from 
the analysis given in my paper on “Canadian Coals,” published 
in the transactions of the North of England Institute of Mining 
Enoineers, for the year 1878. 
Art. VI.—-ON THE RESISTANCE TO THE PASSAGE OF THE ELECTRIC 
CURRENT BETWEEN AMALGAMATED ZINC ELECTRODES AND 
SOLUTIONS OF ZINC SULPHATE. By Pror. J. G. MacGRreEcor, 
M.A., D.Sc., F.R.S.E. 
(Read April 9th, 1883.) 
Arter attention had been directed to the measurement of 
resistance by the establishment of OHm’s Law, the question was 
raised whether or not there was at the surface of separation of con- 
ductors of different substances a special resistance to the passage 
of the current, such that the current was weakened by the mere 
transition from the one conductor to the other. PoGGENDORFF* 
settled this question for metals by so arranging two circuits 

* Poge. Ann. LIT (1841). 
