MEASUREMENT OE TEMPERATURE. 
185 
whole work of the reduction of a single complete observation. The method of 
observing is as follows :—When the temperature is nearly steady, the approximate 
resistance having been ascertained, the galvanometer circuit is closed and the moment 
observed when reversing the battery current with the rocking commutator does not 
affect the galvanometer ; the simultaneous reading x of the U gauge and the time 
are recorded, and the readings of the manometer and barometer are taken. 
The column 6 gives the absolute temperature corresponding to the mean corrected 
pressure P ; t the temperature Centigrade =0 — 6 {j ; Pt observed the corrected value of 
the resistance reduced to 1 at 0 C C. by dividing by the value of P 0 ; P calculated 
the value of R calculated from the empirical formulae 
. (b) 
K o 
(see page 194), and 
R ai 
S-= «■*». . ..(e 
Observations. —Series I. 
I constructed an experimental instrument in November, 1885, of lead glass at the 
Cavendish Laboratory. It was necessarily imperfect from want of skill in glass 
working, and lack of the requisite assortment of glass tubing, However, it was well 
suited to test the capacities of the method, and the observations taken with it agree 
as nearly as may be expected with subsequent and improved apparatus. Details - 
Y 0 = 32'25 cubic centims., /3 0 — '0378, y = '0000263. 
The observations are not all given, as they are less accurate for several reasons. 
Most of them were taken with the temperature varying rapidly, and the mercury 
manometer belonging to a “Jolly” air thermometer was used, the tubes of which were 
too narrow for purposes of accuracy. Nearly five centims, of the fine wire was out¬ 
side the bulb, and the resistance measurements were rendered less accurate by some 
small thermo-electric effects and a slight uncertainty in the resistance of the connect¬ 
ing wires, and by neglecting to take the temperature of the resistance box. 
The capillary tube was also of the same bore as the tube of the HoSOj, gauge, as 
there was none finer to be had on the spot; this of course renders the volume correc¬ 
tion more uncertain. 
Table A-i. contains all the observations taken when the temperature was approxi¬ 
mately steady. The column R calculated shows how very nearly they agree with the 
formulas. Some of the observations, however, taken when the temperature Avas 
varying rapidly about 250 J C., are nearly two degrees out. 
2 u 
MDCCCLXXX VII. — A. 
