138 THE ANTAKCTIC MANUAL, 
volume is easily measured. Instead of using calipers a fine thread is 
wound ten, twenty, thirty or more times round the bulb, then 
unwound and its length measured; this divided by the number of 
turns gives the circumference of the cylinder. The length of the 
cylinder is then measured, and its ends are assumed to be hemi- 
spherical. With the circumference thus determined, the diameter 
and sectional area are calculated, or, more conveniently, taken from 
tables. The length of the cylinder multiplied by the sectional area 
gives the volume of the cylindrical portion. The two hemispherical 
ends make up a sphere of the same diameter as that of the cylinder, 
and its volume is likewise calculated, or taken from tables. It is 
added to that of the cylinder, and the sum is the volume or displace- 
ment of the bulb. It is convenient to record the measurements in 
terms of the centimetre, and the volume is then given in cubic 
centimetres. The external cooling surface of the bulb is found by 
adding the hemispherical surface of the exposed end to the cylindrical 
surface, which is the product of the leneth of the cylinder into its 
circumference. The area of the external surface is given in square 
centimetres (cm.”). It is important to observe that, when cooling, a 
thermometer loses heat through the whole area of its external 
surface; when receiving heat from a particular direction, as for 
instance, from the sun, the receiving area is, for the cylindrical part 
of the bulb, its length multiplied by its diameter, and for the 
hemispherical ends the area of a great circle of the sphere. 
All these measurements have been carefully made on the bulb of 
the thermometer by Chabaud, col. 4, Table XV. For the deter- 
mination of the circumference, a fine thread was wound forty times 
round the cylindrical part. When unwound it measured 111 cm., 
whence we have: 
Circumference . . a ee a Oy 2°775 em. 
Diameter ; é 5 < » +  0°883 em. 
Circular area of cylinder . . . » . .  0°6124 em? 
Length of cylinder. . soe ee we ee) 4°08 cm. 
Volume of cylinder. . . . . 4°08 x 0°6124 = 2°498 ee. 
Volume of sphere 0°883 cm. in diameter . . . 0°877 ce. 
Whence total volume of bulb. . 2 2. 1. . .) 2°875 ee. 
Water value ofbulb . . . . 0°475 x 2875 = 1°366 grins, 
It will be seen that by mensuration we arrive at 2°875 cc. as the 
volume of the bulb in place of 2-835 ce. as derived from the weights 
supplied by the maker. The difference, 0:04 cc., is under 14 per 
cent. of the whole volume. Applying 0-475 as the specific heat per 
unit volume of the bulb, we obtain for the water value 1:366 in 
place of 1°338 grs., a difference of 0°028, which is just 2 per cent. 
