Mr Miller on the Temperature of Mines. 243 
the ventilation still goes on, I believe it will be found that they 
do not lose more of their temperature than can be placed to the 
abstraction of the other causes of heat in working mines, such as 
that produced by the men, and the lights. 
The exact quantity of heat given out by air, in proportion to 
its condensation, it is difficult to ascertain, but every day’s ex- 
perience proves it to be very considerable ; and, I believe, this, 
added to the other obvious sources of heat in mines in a state of 
working, will be found sufficient to account for their high tem- 
perature. 
Art. YIII . — Tables of the Variation of the Magnetic Needle in 
different parts of the Globe . 
The interest which has been recently excited by the great 
discoveries in electro-magnetism, and the probability that the 
meteorological and magnetical phenomena of our globe have 
some strong bond of connexion, render it desirable that the va- 
rious observations on the Variation and Dip of the Needle should 
be collected together. Professor Hansteen of Christiania, from 
whose interesting work on the Magnetism of the Earth we 
have already made copious extracts * (the only ones, indeed, 
that have yet appeared in our language), has collected almost 
all the observations that have been made up to the year 1818 , 
when his work was completed. 
We shall therefore translate his Tables, so far as they go, 
and then add all those observations which have been made du- 
ring the last six years. We have omitted the names of the ob- 
servers as unnecessary, and also the longitudes and latitudes of 
the places of observation, as every person can readily obtain this 
information from ordinary works, and as the insertion of them 
at present would swell the Tables to a length that would have 
rendered them quite unfit for the pages of a periodical work. 
Q 
2 
See this Journal , Vol. Ill, p. 124. ; Vol. IV. p. 114. and 363. 
