220 
MR. H. L. CALLENDAR ON THE PRACTICAL 
Correction for pressure of acid in gauge, -j- *670. 
Corrected value of pressure of air in thermometer, 78‘146 cm. 
The value of the constant mk was calculated each day by Formula I. from the 
observations at air temperature and at the fixed points, assuming the values 
d 0 = 272 o, 90 C., V 0 = 63‘29 c.c. By observing the resistance of the platinum spiral 
the temperature of the air in the bulb could be very accurately deduced. On the 
morning of February 28 the value of mk observed was 10’578, Obs. ( 2 ), and next 
morning 10'577, Obs. ( 8 ). The agreement is very satisfactory, and perhaps closer than 
we have any right to expect, owing to the uncertainty of the pressure measurements. 
Using this value in Formula II., we obtain 
mkjp = T3535 ; 6 = V /{mkjp — X {v/6')} = 821°*6 C. ; 
t = 821-6 — 272-9 = 548°-7 C. ; d = t — pt = 40°-3 C. 
This value is represented by the cross marked (5) on the curve of difference of 
temperature, Plate 13. All the observations in this series were calculated in this kind 
of way ; but, of course, the work was done on a regular systematic form, which 
ensured accuracy and rapidity, so that it should be free from serious errors. 
Graphic Representation of Results. 
The best method of representing the results graphically is that which Pegxault 
adopted in his comparison of mercury thermometers, namely, that of drawing the 
curve of difference of temperature. This has the advantage of indicating all errors 
and deviations on a very large scale. In the curve diagram, Plate 13, fig. 9, the abscissa 
represents temperature Centigrade by air thermometer on a scale of 10 ° to ^-inch, and 
the ordinate the difference of temperature between the platinum and air thermometers 
at the rate of 1 ° to ^-inch. # On this scale errors of 1 in 10,000 are distinctly appre¬ 
ciable in the upper part of the scale, as they correspond to a distance of ^-inch or 
T-millimetre. Observations taken near the standard pressure of 76"0 cm. in Series V. 
are represented by large crosses ( + ); observations at other pressures by small crosses 
(X ). The Arabic numbers belong to Series Y. ; the Homan numbers to other series. 
If the variation of P follows the parabolic formula 
B/R 0 = 1 -f at + fit 2 , 
we shall have d — t — pt — S[(£/ 100) 2 — (^/l 00 )], where 8 = — 10,000 (3/ (a + 100/3). 
The parabola in Plate 4 corresponds to the value 8 = + 1*57. 
Since a + 100/3 = '0033947, 
this gives a = + -0034480, (3 = — *000000533, but the change of resistance does 
not seem to follow this law with absolute accuracy. 
Observation (l) was taken within an hour of drying the air thermometer by 
repeated exhaustion and re-admission of clean dry air at 550° C. 
* The curves are reduced to half-size in the plate. 
