CHEMICAL AND PHYSICAL NOTES. 121 
series made under favourable circumstances at sea generally agree 
more closely with the mean than is the case with a series made 
under similar circumstances on land. The limit to the amount of 
motion with which trustworthy observations can be made does not 
depend on the hydrometer, but on the observer. When the motion 
goes beyond a certain amount of violence, the observer's attention is 
entirely taken up in looking after his own stability, and in preventing 
collision with the swinging table. 
“Tn the Prinecsse Alice I frequently compelled myself to observe 
when the motion was violent, and then kept the waters for observa- 
tion under more favourable circumstances. I rarely found any sensible 
difference in the results; but the labour of making the observations 
in bad weather is very great, and has an irritating effect. In the 
Challenger there was no difficulty in deciding whether the observa- 
tions should be proceeded with or not, because there was no difficulty 
in making them in weather that admitted of the main-deck port, 
which lighted and ventilated the laboratory, being kept open. When 
it was shut, the darkness put a stop to such observations indepen- 
dently of the motion. 
“Tt is, perhaps, not wholly unnecessary to point out that to obtain 
good results with a method such as this the observer must have a 
certain amount of dexterity and patience, but more particularly he 
must approach the matter with the desire to succeed. There is never 
avy difficulty in making unsuccessful experiments. 
“The following table gives the results of determinations of specific 
gravities of samples of Mediterranean water collected in 1893 by 
H.S.H. the Prince of Monaco, which happened to be made at identical 
TapsLe X. 
verte] gee ay [age ae [mee | Sa |e 
an 2 1 oO | 
8 | 6 | 8-05 | 1030156) 16 | 56a) 1 | 10-00 | 1029944 0 
1 | 8-20 140 6 | 10°05 O44 
ai | 4 | 860 | dosnet2 | a5 | a | 2 | 10-00 | 1030271 | 27 
6 | 8-05 196 16 | 10°05 4 
56 | 6 | 8-00 | 1030036) 4 | 52 6 | 10-00 | 1-099997 | us 
38 | 8-00 032 1 | 10-00 sod 
51 | 1 | 10-00 | 1-029966] 15 | 20 | 38 | 8-00 | 1-030002 1 
16 | 10°10 951 1 8-10 vol 
28 | 38 | 8-30 | 1-029934| 1 | 204; 6 | 8-70 | 1-020045! 8 
29 | 8-30 285 | 1 38 | 8-75 | 937 | 
