66 
THE VOYAGE OF H.M.S. CHALLENGER. 
Majuilli. 
evaporation in different latitudes, the amount of rainfall and snow, and the quantity 
of water brought down bv the rivers. He observes the difference between the specific 
gravity of fresh-water and that of sea-water, and the difference in their freezing points. 
This latter difference, he says, is owing to the salt of sea- water, which contains a 
something (spiritus) opposed to congelation. 
Marsilli was also one of the first to study the saltness of the sea, and the bitter taste 
of its water. 1 He believes that both are due to the solvent effect of water on the 
Botijl 
substances forming the bed of the ocean. He made experiments with the hydrometer, 2 
..ad found that the deepest waters were heavier than the surface water. He states that 
he drew the water from various depths, but does not describe in what manner. He 
avers that the salt in the surface water of the Mediterranean, at those points where 
rivers and torrents do not mix with it, and where coral is freely developed, is equal to 
-b of the weight, and of the volume, of the water. He attributes the bitter taste of 
the water to the presence of bitumen. 3 
In his paper : Of the Saltness of the Sea, Robert Boyle describes a great number of 
experiments. He personally made a series of observations on the w r ater of the English 
Channel, collecting it from various depths, and observing its specific gravity. The 
samples from beneath the surface were probably procured by means of Hooke’s water- 
bottle, an extremely ingenious valved box, which is fully described and figured in one 
of the early numbers of the Philosophical Transactions . 4 Boyle investigated the 
8altnes3 of the water by a number of processes : he tried the estimation of total 
sul ids by direct evaporation and ignition, but not being satisfied with the result he 
ultimately took the density as an index of the saltness, and determined this either by 
means of a glass hydrometer, by weighing in a phial which was afterwards weighed 
when full of distilled water, or by weighing a piece of sulphur in distilled water and sea- 
water consecutively. 
“ As for the different degrees of the saltness of the sea,” says Boyle, “ I shall deliver 
wh it I have been informed of as briefly as I can. And first, it hath been observed, by 
on to whom I gave a glass conveniently shaped to try the specific gravity of the water, 
that it grew heavier and heavier as he came nearer the line, till within about 30" latitude ; 
1 Ifandli, op. ciL, p. 21. 
’ V :i>illi, op. at, p. 2-2". This important apparatus for ascertaining the specific gravity of sea-water was discovered 
ut tbc f< .rth 'entury f our era. It was made according to the principle of Archimedes. As mentioned by 
«; intli. r C j at., Bd. ii. p. 36G), the invention of this apparatus was discussed by E. A. Gerland (Zur Geschichte der 
Krfiodun,- <1« Araor. t- r , Ann. d. Phytik «. Chemie, scr. 2, Bd. ii. pp. 160 et scq.) and M. Schmidt (Report in 
Phi L Woe k' xoJin/L, Jahrg. iii. p. 1224). The first clear description of this instrument is to be found in the 
f.! - 1 vr of Bi.diop Synmiu* to Hypatia; nothing in the letter, however, suggests that Synesius was the 
no - f the appamt ■ One Khr-tnniiiH, in a poem in hexameters, attributes the invention to Archimedes; others 
•uril - it to I‘n • ; inui*. It is quite possible that neither of them invented it, but the inventor, whose name is 
unknown, may have lived between 200 and 400 of our era. 
* Marsilli, op. cit, p. 13. 
• l -\l Irani., vol. u p. 439, 1C67 (reproduced in the tail-piece to this Introduction). 
