THE MASS OF A CUBIC INCH OF DISTILLED WATER. 
333 
The cylinder Q was adopted as a solid gravimeter because the density and expansion 
of quartz are well known, as well as on account of the hardness of quartz, its 
capability of receiving a high polish and absence of hygroscopic properties. Q is a 
pure crystal, and was originally adjusted under the directions of Dr. Voit, its coeffi¬ 
cient of linear expansion for 1° C. being taken as 0'00000781 in a direction parallel to 
the principal axis of the crystal. 
The third gravimeter S, is a hollow brass sphere, having on its surface two engraved 
lines for the purpose of linear measurement, and its approximate diameter is six 
inches. 
Water, 
Expansion of Water .—As the weighings of the gravimeters in water could not be 
actually made at the normal temperature of 62° Fahr., corrections were necessary for 
the density of water at various temperatures. There has not yet been made any 
determination of the rate of expansion of water which might alone be accepted, 
and we have therefore to adopt the mean result of several selected determinations. 
Rossetti has stated the result of his experiments (‘ Atti del Istituto Veneto,’ 
1867-8), as well as those of Kopp (1847), Pierre (1845, 1852), Despretz (1839), 
Hagen (1855), and Mattiiiessen (1866), in a table which gives 1 ’001121 as the 
ratio of the density of water at 62° Fahr. (16°*6 C.) to its maximum density at 4° C. 
It does not appear 'whether Rossetti corrected the earlier results by more recent deter¬ 
minations of the rates of expansion of mercury and of glass; which corrections at 
some temperatures would affect the last place of decimals in the above expression 
(FOOl 121). The differences between the above determinations would also affect the 
present investigation to 0'0009 grain in the mass of the cubic inch of water. 
In 1870 Dr. Foerster,* after a critical examination of the results above referred 
to, as well as of those of Jolly (1864) and W. H. Miller (1856), t adopted the mean 
results of Miller and Rossetti (after Schiaparelli, 1868); which give 1'001 118 
as the ratio at 62° Fahr. ; or if the maximum density of water is taken at the 
temperature of 4° C., then at 62° Fahr. the density of water may be expressed by 
0'998881 ; and these mean results have, therefore, been followed in the present 
investigation. 
* ‘ Metronomische Beitriige,’ No. 1, Berlin, 1870. 
t ‘Phil. Trans.,’ 1857 (Part III. for 1856). 
