122 
Di;. M. w. ti;avei;s, mi g. sextei;, axd de. a. jaquekod 
'i’u shield the apparatus against radiation from the heated vessel a piece of vood, 
kept v et Ijy a stream of water, was used as a screen. A similar piece of wood, with 
a slit cut in it for the stem, was held in a clamp horizontally about 1 centini. above 
tlie to}) of the hy|)someter to screen the horizontal })ortion of the stem. The 
tem}jerature of the short length of stem between the hy}jso)neter and the screen 
was usuallv about t)G°, a ditference from 100"^ too small to be considered. During 
each ex})eriment the barometer was always read three times ; at the beginning, at 
the end, and between the two })airs of observations. 
18. Calculation of the Residts. 
In calculating the value of the pressure coetiicient from the results of our 
e.\})eriments, we em})loyed the usual methods. The })ressure and Avhich the 
gas AV(.)uld exert at the tem})erature of melting ice, and at that of saturated water 
A a])our at the normal })ressure, if confined in a S})ace corres}Jonding to the volume 
of the thermometer at 0° C., were first calculated. The })ressure coefficient was then 
obtained from the equation 
a = (P^oo — l^o)/ i^ioo • 
In calculating P^ and P^^^ it is of course necessary to assume some value for the 
})i'essure coefficient in order to ai)})ly the necessary correction for the gas contained 
in the stem and dead-s|jace; and in reducing the tenqjerature of the bulb to 100° C. 
in calculating These corrections are, however, small; and no a}:»})reciable error 
is introduced by taking the coefficient as 1/273. 
The follov'ing equations were enqdoyed in calculating P^j and P^qjj :— 
l‘„ = 
,, , V, X 273 , V,/. X 273 
I 2(0 + 1 , 2(.3 + i, 
1 
V 
P — P' 
lou — -L 
.) ( o 
273 + 
IX I X 373 y,/, X 373 
r\y 0“*'‘ I , riy 
AVI I ere T is the observed })ressure at the ice-})oint. 
P' is the observed })ressure at the steam-})oint. 
T is the tenq)erature of steam corres})onding to the barometric })ressure. 
Tbaiul TV are tlie tem})eratures of the stem. 
TVs and T,V are the tem})eratures of the dead-s})ace. 
AV is the volume of the bulb at the ice-point. 
A is the volume of the bulb at the steam-})oint. 
AV iw the volume of the stem. 
A,/,, is the \'olume of the dead-s}3ace. 
A" = (Vi + AV + V,/,.), is the total volume of the thermometer at 0° G. 
'I'lie method by which the tem})erature, })ressure, and ^■olume were calculated and 
corrected has already been dealt \vith. 
