REPOET ON THE SPECIFIC GRAVITY OF OCEAN WATER. 
11 
Hubbard believed from bis experiments that, for all ordinarily occurring ocean waters 
the volume ratios were the same. The later observations of Thorpe and Rucker, Ekman, 
Torn0e, and Dittmar have shown that this is not strictly the case. 
In the Meteorological Observations published in the second volume of the Narrative, 1 
the specific gravities are reduced by Hubbard’s Tables, the reductions having been per- 
formed during the cruise. The specific gravities in the following tables have been reduced 
by the table compiled by Prof. Dittmar. 2 They are therefore free from the error attaching 
to Hubbard’s experiments. The results of Prof. Dittmar’s Table are shown graphically in 
PI. I., in which specific gravities at the temperature of observation are ordinates, and 
those at 15°‘56 C. are abscissae; the diagonal lines are isothermals, showing the variation 
of observed and reduced specific gravities for every degree of temperature. This chart 
enables reductions to be carried out rapidly and easily by inspection. For instance, let 
the density observed at 3° C. be 1 ‘02800. Find the point on the isothermal of 3° C. 
whose ordinate is 1 ‘02800, its abscissa is 1 ‘02600, and that is the density at 15°‘56 C. 
For a discussion of the observations by various experimenters on the expansion of sea- 
water, the reader is referred to Prof. Dittmar’s Report on the Composition of Ocean Water. 2 
In order practically to test the accuracy of the observations, occasion was taken when 
the temperature and salinity of the water were such as to immerse nearly the whole 
stem, when weight No. v was used, to take a reading immediately afterwards with 
weight No. iv, which immersed very little more than the body of the instrument. The 
effect of this was to obtain two observations of the density of the same water at the same 
temperature, one from a reading near the top of the scale, and the other from one near 
the bottom (Table VIII.). 
Table VIII. 
Giving Duplicate Observations op the same Sample of Water with the same 
Hydrometer differently Weighted. 
No. of 
Sample. 
Density 
observed with 
Differ- 
ence 
OOiv- 
OOv. 
No. of 
Sample. 
Density 
observed with 
Differ- 
ence 
OOiv- 
OOv. 
OOiv. 
OOv. 
OOiv. 
OOv. 
120 
1-02412 
1-02411 
+ 1 
274 
1-02416 
1-02412 
+ 4 
127 
1-02414 
1-02409 
+ 5 
826 
1-02411 
1-02411 
0 
135 
1-02406 
1-02413 
-7 
829 
1-02411 
1-02408 
+ 3 
139 
1-02407 
1-02414 
-7 
830 
1-02400 
1-02405 
-5 
181 
1-02428 
1-02427 
+ 1 
831 
1-02411 
1-02418 
+ 3 
The agreement between these results, dependent only on the hydrometer and the 
accuracy of observation, gave me much confidence in the correctness of my work. 
1 Narrative, Cliall. Exp., vol. ii. pp. 300-744. 2 Phys. Chem. Cliall. Exp., part L 
