Phosphorescence of the Sea 511 



Descartes' idea was that when a wave hits an obstacle, the motion 

 that the agitation imparted to the particles of salt caused them to 

 separate from the particles of water and to 



generate sparks rather similar to those which are emitted by pieces of 

 flint when they are struck. In truth, to produce that effect these salt 

 particles must be very straight and smooth so that they may more easily 

 separate themselves from the particles of fresh water. This explains why 

 brine or sea water which have been kept a long time in some container 

 are not suitable for that experiment. Furthermore, the particles of fresh 

 water must not be too closely packed (pressed) around the salt particles. 

 This explains why these sparks are more often observed in warm than 

 in cold weather and when the sea is somewhat rough, and also why fire 

 does not issue from all the waves. Finally the salt particles must have a 

 straightforward motion, like arrows and not move crosswise, this being 

 the reason why all the drops which spurt out of the same water do not 

 shine with the same brightness.^ 



It is not surprising that Jacques Rohault (1620-1675) , as the 

 foremost protagonist of Cartesian philosophy should have dealt with 

 the light of the sea in a very detailed manner, especially interest- 

 ing for comparison with Decartes' earlier phraseology. Rohault's 

 opinions are expressed in his Traite de Physique (1671) in a chap- 

 ter dealing with salt, but which also includes various phenomena 

 connected with the sea. The quotations printed below are from the 

 English edition, Rohault's System of Natural Philosophy " done into 

 English by John Clarke with Samuel Clarke's notes taken mostly 

 out of Sir Isaac Newton's philosophy, with additions," London, 1723 

 (Part III, Chap. 4, Sec. 14-17). 



Rohault answered four questions regarding the shining of the 

 sea, all of them quite uninfluenced by Newton's views, as follows: 



Why the water of the sea shines when it is in violent Agitation. 



Salt being then of such a Nature as we have described, it is not at all 

 strange that when the Waters of the Sea are violently agitated in a very 

 hot Season, its Waves should ^ throw out an infinite Number of Sparks 

 in the Night into the Air. For we ought to consider, that these Waves 

 must disperse a great many Drops about in the Air, which divide them- 

 selves into still smaller Drops; and that some of the Particles of the 

 Salt, which are the most solid and most agitated, may then disengage 

 themselves from the Parts of the Water, and dart themselves into the Air 

 with their Points forward in such a manner as to be surrounded only 

 by the Matter of the first Element, which may communicate a force to 

 them sufficient to impel the second Element, and so produce Light. 



' Clarke quoted Newton on " Sea Water in a raging Storm," query 8 of Newton's 

 Opticks (1718). 



