6 
THE VOYAGE OF H.M.S. CHALLENGER. 
Table IV. 
(Jiving the Correction to be added to the Immersed Volume of the Hydrometer 
FOUND FROM TABLE III., FOR EVERY DEGREE CENTIGRADE FROM 1° C. TO 30° C. 
Temp. 
*C. 
Volume 
c,c. 
Temp. 
°C. 
Volume 
c.c. 
Temp. 
°C. 
Volume 
c.c. 
Proportional parts for 
Tenths of a Degree. 
I 
1 
00046 
11 
0-0502 
21 
0-0958 
o 
0-1 
0-0005 
2 
0091 
12 
0547 
22 
1003 
2 
0009 
3 
0137 
13 
0593 
23 
1049 
3 
0014 
4 
0182 
14 
0638 
24 
1094 
4 
0018 
5 
0228 
15 
0684 
25 
1140 
5 
0023 
6 
0274 
16 
0730 
26 
1186 
6 
0027 
7 
0319 
17 
0775 
27 
1231 
7 
0032 
8 
0365 
18 
0821 
28 
1277 
8 
0037 
9 
0410 
19 
0866 
29 
1322 
9 
0041 
10 
0456 
20 
0912 
30 
1368 
... 
... 
By means of these two tables the volume of water displaced at any temperature can 
l»e found. It has been observed above that the hydrometer, as it stands and without any 
added weight, would be useful only through a very limited range of densities. Its weight is 
IGO'2128 grms., and the total volume of the divided stem is 0 '8 65 c.c., that of the body of 
the instrument being at ordinary temperatures 160-35 c.c. We have thus an extreme range 
in volumes of 1G0'350 to 16r206 c.c., and by consequence in density of CU99914 to 0'99384, 
equal to 0 0053. Were the density of the water dependent solely on its saltness, 
this range would have sufficed for all the waters met with during the cruise. That is to 
say, the extreme range of specific gravities at constant temperature was not greater than 
0 0053. The range is doubled when the effect of variation of temperature is remembered, 
and it is still further extended when account is taken of the condensation produced by 
tin* pressure of the overlying water at the bottom and intermediate depths. In order to 
make it possible, by means of the hydrometer above described, to observe all densities 
from that of distilled water up to that of the densest sea- water, a small brass table was 
made to fit on to the top of the stem of the hydrometer. Its weight was 0'836 grm., so 
that when the instrument was floating in distilled water of about 16° C. at about 97 mm., 
it depressed it to about 1 mm. A series of six weights were then made, each as nearly as 
pofsibh- a simple multiple of the weight of the table. It is not necessary that they should 
In- exact multiples, they arc brought approximately to the desired weight, and then their 
a< tual weight is accurately determined on the balance. The following are the weights 
which were used : — 
II. III. IV. 
1-6010 2-4225 3-2145 
No. 
Weight grm*., 
I. 
0-8560 
v. 
4-0710 
VI. 
4-8245 
