168 
THE FHYSIGAL GEOGRAPHY OF THE SEA. 
shells and marine insects could not operate upon the specific grav- 
ity of its waters, nor give variety to its climates; neither could 
evaporation give dynamical force to its circulation, and they, ceas- 
ing to contract as their temperature falls below 40°, would give 
but little impulse to its currents, and thus its circulation would be 
torpid, and its bosom lack animation. 
337. This under current may be freighted with heat to temper 
some hyperborean region or to soften some extra-tropical cli- 
mate 64), for we know that such is among the effects of ma- 
rine currents. At starting, it might have been, if you please, so 
loaded with solid matter, that, though its temperature were 70°, 
yet, by reason of the quantity of such matter held in solution, its 
specific gravity might have been greater even than that of extra- 
tropical sea water generally at 28°. 
338. Notwithstanding this, it may be brought into contact, by 
the way, with those kinds and quantities of marine organisms that 
shall abstract solid matter enough to reduce its specific gravity, 
and, instead of leaving it greater than common sea water at 28°, 
make it less than common sea water at 40° ; consequently, in 
such a case, this warm sea water, when it comes to the cold lati- 
tudes, would be brought to the surface through the instrumentality 
of shell-fish, and various other tribes that dwell far down in the 
depths of the ocean. Thus we perceive that these creatures, 
though they are regarded as being so low in the scale of creation, 
may nevertheless be regarded as agents of much importance in 
the terrestrial economy ; for we perceive that they are capable of 
spreading over certain parts of the ocean those benign mantles of 
warmth which temper the winds, and modify, more or less, all the 
marine climates of the earth. 
339. The makers of nice astronomical instruments, when they 
have put the different parts of their machinery together, and set 
it to work, find, as in the chronometer, for instance, that it is sub- 
ject in its performance to many irregularities and imperfections — 
that in one state of things there is expansion, and in another state 
contraction among cogs, springs, and wheels, with an increase or 
diminution of rate. This defect the makers have sought to over- 
come ; and, with a beautiful display of ingenuity, they have at- 
tached to the works of the instrument a contrivance which has 
had the effect of correcting these irregularities, by counteracting 
