SEPTEMBER 24, 1897. ] 
the rate of variation of specific heat with 
temperature, which could be determined in- 
dependently of the absolute value of the 
Clark cells used in the work. It is also of 
special interest in connection with the re- 
cent proposal of the Electrical Standards 
Committee of Section A to adopt the Joule 
or Watt-Second as the absolute unit of heat. 
According to the most recent reductions, 
the result of Rowland by the mechanical 
method, and of Griffiths and Schuster by 
the electrical method, for the specific heat 
of water differ by about one part in 400. 
This discrepancy is possibly due to an error 
in the value assumed for the Clark cell, but 
it is interesting to verify the comparison by 
a totally different method of calorimetry, to 
avoid any possible errors which may have 
remained unsuspected in the ordinary 
method, in which a known mass of water is 
heated through a certain range of tempera- 
ture. In the method of Callendar and 
Barnes the temperature conditions are ex- 
tremely steady, and observations can be 
taken under the most favorable conditions. 
The external loss of heat is reduced to a 
minimum by means of a vacuum jacket, 
and can be very accurately measured by 
varying the electric current and the flow of 
liquid in a suitable manner. Since there is 
practically no change of temperature, the 
correction for thermal capacity of the 
calorimeter is negligible. 
A crowded audience assembled to hear 
Lord Kelvin on the ‘ Fuel and Air Supply 
of the World.’ The address, which lasted 
about half an hour, was very characteristic, 
especially in the humorous attack on the 
English system of measures. Assuming 
that the earth was originally ata high tem- 
perature, and that there was at first no free 
oxygen in the atmosphere, it may be con- 
eluded with a high degree of probability 
that the present store of oxygen has been 
evolved by the action of sunlight on vege- 
tation. ‘To every three tons of oxygen there 
SCIENCE. 
467 
corresponds on the average one ton of coal 
or of fuel derived from vegetation. As there 
are at present two tons of oxygen to every 
square meter of the earth’s surface, the total 
oxygen supply may be estimated at about 
one thousand million million tons, and the 
total fuel supply at 340 million million tons. 
According to the estimates of the Coal Sup- 
ply Commission of 1831, it appears that Eng- 
land, with an area equal to one two-thous- 
andth part of the earth’s surface, possesses 
more than its share of fuel, the greater part 
of which is available for working. As the 
coal is used up, if it were not for increasing 
vegetation, we should be more likely to die 
from want of air than from want of coal. 
Dr. Alexander Johnson, of McGill Col- 
lege, followed with a plea for an Imperial 
Hydrographic Survey. A committee of the 
British Association appointed at his sugges- 
tion in 1884 had succeeded in inducing the 
Canadian government to make a grant for 
the promotion of tidal observations. This 
grant has recently been reduced, and there 
was some risk that it might be discontinued 
altogether at a time when such observations 
were of special importance. At Professor 
Johnson’s request an influential committee 
was again appointed to seek the cooperation 
of the Admiralty in establishing a perma- 
nent department. 
Professors Hwing and Dunkerley, of Cam- 
bridge, England, contributed a paper on 
the ‘Specific Heat of Superheated Steam.’ 
They adopted the method of the throttling 
calorimeter, which is not so well known in 
England as in America, but instead of de- 
termining the wetness of the steam in terms 
of the degree of superheating observed they 
used a separator, and assuming the steam 
to be dry, deduced the value of the specific 
heat. A roll of silk was used, following 
Thomson and Joule, instead of an aperture 
for throttling the steam. 
Professors Runge and Paschen contrib- 
uted a note in continuation of their well- 
