CHAP. L.] THE EQUIPMENT OF THE SHIP. 57 
For use, a curve is laid down, giving the volume of the stem 
for every division of the scale, measured from the lowest one, 
and another curve, giving the volume of the body of the instru- 
ment, upon the lowest division of the scale in the stem, for dif- 
ferent temperatures. When, therefore, in calculating the spe- 
cific gravity of a liquid, we require to find the volume of the 
instrument immersed, from the one curve we get the volume of 
the stem, and from the other that of the body of the instrument 
immersed. The sum of the two gives the volume of the liquid 
displaced. The weight em vacuo of the hydrometer, together 
with plate and weight divided by the volume so found, gives 
the specific gravity of the liquid for the temperature during 
observation, that of water at 4° C. being unity. 
The instrument at present in use has the following elements: 
Weight of hydrometer a wacuo............-.----+-- 160.2128 grammes. 
Wielshtiotrtable my siyAin weit ile. coche cle lect oueee wievers 0.8360 6 
WicimhtzolmVVel@ hin iy sees tcl ibap.1e. ox aelan'<netegeieel pas 0.8560 c 
ae SPU ee sata raya ch aha ici ame oes aloes 1.6010 nS 
é a, MIM es ratais ws 5, cist Seatac so horses  MeeeaO K: 
i SS MMos cu ceons sr co eteae Sees a aes MeL D . 
PA Rees Beccesoehunhco com Dcice tan ac ae 4.0710 us 
SS Boe WSL 5% tsrcuchaist once se, 950.) Soe eee cia b eee - 
The diameter of the stem is as nearly as possible 3 millime- 
tres, the volume of 100 millimetres (the length of the scale) be- 
ing 0.86 cc. Had the volume of the stem been determined by 
weighing the instrument in water at 4° C. instead of 15° C., 
the volume would have been found to be 0.8607 ec., instead of 
0.86 ce. The difference between the two is wholly inappreci- 
able. 
The volume of the body of the instrument at 0° is 160.3 ce., 
and at 22°.2 160.4, the co-efficient of expansion having been 
found, by immersion in distilled water of different tempera- 
tures, to be 0.000027. 
The bulk and weight of the body, taken along with the slim- 
ness of the stem, make great care in handling it necessary, and, 
