SUMMARY OF RESULTS. 
67 
from whence to Jamaica he observed no alteration in the specific gravity in the leash 
And in confirmation of this I am likewise informed by one, who for his own satisfaction 
weighed the water, both under the Aequinoctial and at Cape of Good Hope, and found 
that the weight of both was the same. To which may be added that it is commonly 
observed at Mozambique, one of the hottest places in the world, that the sea is so salt 
there, that it bears up the ships a considerable height out of the water, more than in 
other places ; and that the water may be much salter in one place than another, by 
having more salt dissolved in it, does not only appear from what hath been said, but also 
from what is frequently observed in the different strengths of brine-pits.” 1 
Halley was of opinion that the saltness of the sea was due to the substances carried Halley. 
down in solution by the rivers. 
The colour and transparency of sea-water were also the subjects of observation. Observations on 
Bouguer, who made experiments on the transparency of the water at Croisic and in ^ e ^ ns ' 
the torrid zone, supposes that a depth of 10 feet of water weakens light at most in of Sea-Water. 
the proportion of 5 to 3, or perhaps 5 to 3-g. 2 He says that the depth at which 
sea- water loses the whole of its transparency will be found to be about 656 feet. 3 
It was recognised even then, however, that the transparency varied at the same depth 
in different seas. Muncke 4 reports the following experiments made last century on 
board the ship “Coquille”: — “To judge of the transparency of sea- water, we used to 
tie a string to a board painted white, and would let it down till we could see it no 
longer. We found that near the island of Waigion it disappeared from sight at a depth 
of 59 feet, and with a very bright sky at 75 '3 feet; near Port Jackson, 38 '3 feet; near 
New Zealand, 35 feet ; and near Ascension between 28 and 36 feet.” There is a very 
wide divergence in the different statements, for Wood, in 1676, observed mussel shells 
on the bottom at 80 fathoms, near Nova Zembla, and Admiral Milne records having seen 
the bottom in the Caribbean Sea at 25 fathoms. 
The celebrated experiment of Halley with the diving-bell seems to have led to the Colour of the 
study of the coloration of the sea. Newton said the colour of the sea was green 
Marsilli thought it was blue, and explained it by the presence of salt in sea-water. This 
writer maintained at the same time that the colour varied in the upper and lower strata 
of the sea. 
As regards the knowledge of marine organisms, Gesner in 1558 published the fourth Marine 
book of his w T ork, 5 which is devoted to the description of fishes and marine animals; and <jR AM ' M ‘ 
John Johnston, who studied at St. Andrews in 1619, published a treatise on aquatic 
1 Boyle’s works, epitomised by Boulton, vol. i. p. 282, London, 1699. 
2 Bouguer, Traitii d’Optique, p. 64, Paris, 1760. 3 J. H. Lambert, Pbotometria, &c., Augsburg 1 7oO. 
4 In Gehler’s Physik. Worterbuch, Aufl. 2, Bd. vi. Abth. iii . p. 1708, Leipzig, 1837. 
5 Gesner, Historic Animalium, Liber iv., Tiguri 1558. 
