THE EARTH. 



73 



I will conclude this chapter with one effect 

 more, produced by the saltness of the sea ; 

 which is, the luminous appearance of its 

 waves in the night. All who have been spec- 

 tators of a sea by night, a little ruffled with 

 winds, seldom fail of observing its fiery 

 brightness. In "some places it shines as far 

 as the eye can reach ; at other times, only 

 "when the waves boom against the side of the 

 vessel, or the oar dashes into the water. 

 Some seas shine often ; others more seldom ; 

 some, ever when particular winds blow ; and 

 others, within a narrow compass ; a long 

 tract of light being seen along the surface, 

 whilst all the rest is hid in total darkness. 

 It is not easy to account for these extraordi- 



nary appearances : some have supposed that 

 a number of luminous insects produced the 

 effect, and this is in reality sometimes the 

 case ; in general, however, they have every 

 resemblance to that light produced by elec- 

 tricity ; and, probably, arise from the agita- 

 tion and dashing of the saline particles of the 

 fluid against each other. But the manner in 

 which this is done, (for we can produce no- 

 thing similar by any experiments hitherto 

 made,) remains for some happier accident to 

 discover. Our progress in the knowledge 

 of Nature is slow ; and it is a mortifying 

 consideration, that we are hitherto more 

 indebted for success to chance than 

 d us try. 



in- 



CHAPTER XVI. 



OF THE TIDES, MOTION, AND CURRENTS OF THE SEA; WITH THEIR 



EFFECTS. 



IT was said, in the former chapter, that the i 

 waters of the sea were kept sweet by their 

 motion, without which they would soon pu- 

 trefy, and spread universal infection. If we 

 look for final causes, here, indeed, we have 

 a great and an obvious one that presents itself 

 before us. Had the sea been made without 

 motion, and resembling a pool of stagnant 

 water, the nobler races of animated nature 

 would shortly be at an end. Nothing would 

 then be left alive but swarms of ill-formed 

 creatures, with scarcely more than vegetable 

 life ; and subsisting by putrefaction. Were 

 this extensive bed of waters entirely quies- 

 cent, millions of the smaller reptile kinds 

 would there find a proper retreat to breed 

 and multiply in ; they would find there no 

 agitation, no concussion in the parts of the 

 fluid to crush their feeble frames, or to force 

 them from the places where they were bred ; 

 there they would multiply in security and 

 ease, enjoy a short life, and putrefying, thus 

 again give nourishment to numberless other, 

 as little worthy of existence as themselves. 



Boyle, vol. i. p. 294. 



But the motion of this great element effectu- 

 ally destroys the number of these viler crea- 

 tures ; its currents and its tides produce con- 

 tinual agitations, the shock of which they 

 are not able to endure; the parts of the fluid 

 rub against each other, destroy all viscidi- 

 ties ; and the ocean, if I may so express it, 

 acquires health by exercise. 



The most obvious motion of the sea, and 

 the most generally acknowledged, is that of 

 its tides. This element is observed to flow 

 for certain hours, from south towards the 

 north ; in which motion or flux, which lasts 

 about six hours, the sea gradually swells; so 

 that entering the mouths of rivers, it drives 

 back the river waters to their heads. After 

 a continual flux of six hours, the sea seems 

 to rest for a quarter of an hour; and then 

 begins to ebb, or retire back again, from 

 north to south, for six hours more ; in which 

 time the waters sinking, the rivers resume 

 their natural course. After a seeming pause 

 of a quarter of an hour, the sea again begins 

 to flow as before : and thus it has alternate- 

 ly risen and fallen, twice a day, since the 

 creation. 



