1902— 3. J Mr Manley on Electrical Conductivity of Sea- Water. 357 
Regnault’s method was followed, viz., that of suspending from a 
hook attached to the pan in which the weights are placed a glass 
counterpoise, having as nearly as possible the same weight, area 
and volume as the pyknometer. It was prepared from a suitable 
test-tube, the open end of which was drawn out in the form of a 
capillary tube, and bent hookwise. As the counterpoise when 
first prepared was found to be considerably lighter than the- 
pyknometer, water was introduced into the former until its weight 
was almost but not quite equal to that of the latter ; the capillary 
was then sealed before the blow-pipe. 
5. All the weighings of the pyknometer and contents were 
performed according to the method suggested by Gauss; that is, 
the object was weighed first in one pan and then in the other. 
Since any two individual weighings gave but slightly different 
values, the mean was in every case accepted as the true one. 
6. The volume of the pyknometer which was used is approxi- 
mately 49 c.c. As the weight of this volume of distilled water 
does not greatly differ from that of the same volume of sea-water, 
it is wholly unnecessary to apply a correction for the air displaced 
by the brass weights. Such a refinement would only alter the 
values obtained for the relative densities of the samples of water 
in the sixth decimal place. 
Experiments ivith the Counterpoise. 
With the object of testing the theoretical advantage gained by 
the use of a counterpoise, the pyknometer was charged and then 
carefully wiped with a fine white linen cloth; the counterpoise 
was also wiped at the same time ; they were then placed in clean 
glass beakers within the balance-case. After the expiration of 
five minutes the weight of the pyknometer and its contents wa& 
determined by the reversal method of Gauss, ( a ) with, and ( b ) 
without, the use of the counterpoise. In suspending the pykno- 
meter or counterpoise from the arms of the balance, use was made 
of a small ivory lifter, in order to avoid any direct handling and 
consequent errors. Experiments showed that it was immaterial 
whether the weighings without the counterpoise were made first 
or last ; hence it was concluded that a normal amount of moisture 
condenses upon the pyknometer during the five minutes allowed 
