ox THE MEASUEEHEXT OE TEMPERATURE. 
22, Accuracy of the Results. 
]]i (lesciibiiio- the constructioii of the apparatus and the manner In which the 
experiments were carried out, we have already pointed to the errors which may 
occur and their effect on the accuracy of the final result. It will have been noticed 
that wdth the exception of the errors in the barometer reading, and in the tempera¬ 
ture of the steam in the hypsometer, the errors of observation afiect Pq and Pjijq 
almost equally, and hence have little eftect on the value of the coefficient. Further, 
since an error of OH millim. in the barometer reading only changes the value of 
Pioo (950 millims.) by O'OOo millim., the effect of such an error on the value of the 
coefficient is less than five units in the sixth significant figure. 
With regard to the measurement of the pressure, as we liave already stated, the 
errors in the scale were certainly less than O'Ol millim. An error in the difterence 
PiQQ-Po ffii'‘^ magnitude wmuld involve an error of one unit in the fifth significant 
figure. The actual extreme difference between the value of in the set of three 
observations which constitute each series usually amounts to 0’02 to 0'03 millim., 
but these differences appear to be unbiassed and do not influence the final result in 
one direction or in the other. The value of the temjDerature correction practically 
disappears, for, as we have pointed out, the temperature of the column could be 
determined to (P02° C., and in successive determinations of P^ and P^qo tempera¬ 
tures were practically identical. The capillarity correction involving the height of 
the meniscus we considered at first to have a doubtful clmracter, but as the height 
of the meniscus varied by 0'04 millim. in different observations, and the application 
of the correction brought the observed pressures to tlie same value, we liave come 
to the conclusion that it is sound. 
The errors in the measurement of the volume and temperature of the dead-space 
are small. Tlieir effect on the value of the coefficient has already been sufficiently 
discussed. 
23. Tli,e Final Values for the Pressure Coefficients of Hydrocjen and Helium. 
As tlie tables in Sections 20 and 21 sliow^, w'e have two series of determinations of 
the pressure coefficient both in the case of hydrogen and of helium at initial 
pressure of about 700 millims. of mercury. The results are as follows :— 
Uas. 
Observed values of the coefficient, a. 
Mean value. 
Hydrogen. 
Helium. 
0-00.366261, 0-003662.52 
0-00366241, 0-00366270 
0-00366255 
0-003662.55 
