rendered barter and commerce possible, but its apparently boundless 
immensity probably first suggested the idea of infinity, and thus 
led to the conception of an Omnipotent and Omniscient Being. To 
the ocean we are indebted for the first naturalists, in the persons 
of the primitive fishermen, who cast their nets in the creeks of the 
Cyclades, and the ancient Pheenician sailors were undoubtedly the 
first of marine engineers. The ocean covers no less than three- 
quarters, or, to be quite correct, eight-elevenths of the surface of 
the earth, indeed if the earth were of one uniform level it would be 
entirely submerged in the sea to a depth of 600 feet. The average 
depth of the sea is about 2,000 feet, ranging from a mean of 180 
feet in the Baltic to 14,500 feet in the Atlantic and 15,400 feet in 
the Pacific. One reads sometimes of vast abysses and unfathom- 
able depths of ocean, but the soundings taken by Maury and others 
prove that there exists nowhere a greater depth than five miles. 
It is true that a lead line may run out for 40,000 or 50,000 feet, or, 
indeed, indifinitely, without touching bottom, but this is because 
the undercurrents of the deep sea have power to bear the line off 
longitudinally, long after the plummet has ceased to sink. The 
ocean is continuous all over the earth, and practically maintains the 
same level, contrary to the belief held not long since that the 
Mediterranean and some other inland seas were ofa higher level 
than the open ocean. The bulk of the ocean is so great that it has 
been calculated if all the enormous basins which it now fills were 
empty, it would require 40,000 years for all the rivers of the earth 
to re-fill them. 
Sea water, when pure, is the most perfectly transparent of all 
fluids, as I daresay many of you haye found out to your cost when 
you have stepped into one of the transparent pools often, found 
among the rocks at low water. This transparency is of course 
relative, not absolute, and ceases entirely at a certain depth. Many 
experiments have been made by Professor Tyndall, Pere Secchi, 
and others, to measure the extent of this transparency by sinking 
white plates and various coloured discs attached to a string 
beneath the surface of the sea, and noting the depth at which they 
ceased to be visible. It was found that a white disc 12ft. in 
diameter appeared light green at the depth of a few feet, then blue 
green, later dark blue, and finally disappeared from view at a depth 
of 126 feet.. Discs of yellow or brown disappeared much more 
quickly. These experiments were made in the transparent waters 
of the Mediterranean, and under a bright sunny sky, @.e., under 
the most favourable circumstances. Now, as the bottom of the 
sea is never absolutely white, and if it were, could not possibly be 
seen at a greater depth than about 180 to 140 feet, it is difficult 
to believe the wonderful stories told by travellers of ocean bottoms 
