1879.] 
British Association. 
683 
The Report of the Committee for making more accurate 
determinations of the mechanical equivalent of heat stated 
that the work in progress was the protracted one of sup- 
plying a means of correcting errors in the determination of 
the temperature arising from the temporary changes of the 
fixed points of thermometers constructed of glass. An 
extensive series of experiments had recently been made by 
Prof. H. A. Rowland, of Baltimore, who, being unaware 
of what had been done by the Committee, had arrived at 
an equivalent almost identical with that determined by 
Mr. Joule. 
The Report of the Committee for procuring Reports on 
the Progress of Mathematics and Physics contained two 
communications to the Committee, the one from Prof. Clerk- 
Maxwell, F.R.S., and the other from Prof. Stokes, F.R.S., 
giving their opinions on the questions with which the Com- 
mittee has to deal. 
The Twelfth Report of the Committee on Underground 
Temperature was read by Prof. J. D. Everett, F.R.S. One 
of the methods employed for taking underground tempera- 
tures is the lowering of maximum thermometers into deep 
bore holes filled with water. Another mode is to take ob- 
servations in mines and collieries of the readings of very 
slow-aCting thermometers. The experiments referred to 
include those of Dr. Stapff, made in the St. Gothard Tunnel. 
The mean temperature gradient for the whole length of the 
tunnel (about 9 miles), was found to be i° F. for every 
88 feet, but Dr. Stapff found that where the surface of the 
upper ground is a steep ridge the temperature gradient is 
less rapid than that, which is quite consistent with the hypo- 
thesis that the earth was at one time very much hotter than 
it is now, and that it is undergoing a process of cooling 
down. 
The Report of the Committee on Atmospheric Electricity 
in Madeira was read by Dr. M. Grabham. Observing the 
regular winds and breezes, Dr. Grabham traced the steady rise 
of electricity in the early morning to a maximum at 11.30 
a.m., which declines after much steadiness for two hours, at 
first suddenly, and then very gradually towards night. 
The Report of the Committee on Luminous Meteors — 
read by Mr. James Glaisher, F.R.S. — dealt in detail with 
the accounts of conspicuous detonating fire-balls that had 
occurred in the United States on August nth and Decem- 
ber 18th, 1 878, and on January 27th, 1879 ; in Bohemia and 
Saxony on January 12th, 1879 ; and in England on February 
