520 History of Luminescence 



sent to England in 1749, I considered the sea as the grand source of 

 lightening, imagining its luminous appearance to be owing to electric 

 fire, produc'd by friction between the particles of water and those of 

 salt. Living far from the sea, I had then no opportunity of making 

 experiments on the sea water, and so embraced this opinion too hastily: 



For in 1750 and 1751, being occasionally on the sea coast, ^^ I found, 

 by experiments, that sea water in a bottle, tho' at first it would by agita- 

 tion appear luminous, yet in a few hours it lost that virtue; hence, and 

 from this, that I could not by agitating a solution of sea salt in water 

 produce any light, I first began to doubt of my former hypothesis, and 

 to suspect that the luminous appearance in sea water, must be owing to 

 some other principles. 



In 1753, a letter (No. VII) from J. B. Esq. (James Bowdoin 

 (1727-1790) of Boston, Governor of Massachusetts) to B. F., pub- 

 lished in Franklin's Experiments and Observations on Electricity 

 made at Philadelphia in America, to which are added Letters and 

 Papers on Philosophical Subjects (1769) , pointed out that the light 

 in sea water could be removed by filtering through a cloth and 

 that the 



said appearance might be caused by a great number of little animals, 

 floating on the surface of the sea, which, on being disturbed, might, by 

 expanding their finns, or otherwise moving themselves, expose such a 

 part of their bodies as exhibits a luminous appearance, somewhat in the 

 manner of a glow-w^orm, or fire-fly. . . . 



Franklin ^^ replied as follows: 



... It is indeed very possible, that an extremely small animalcule, too 

 small to be visible even by the best glasses, may yet give a visible light. 

 I remember to have taken notice, in a drop of kennel water, magnified 

 by the solar microscope to the bigness of a cart-wheel, there were num- 

 bers of visible animalcules of various sizes swimming about; but I was 

 sure there were likewise some which I could not see, even with that 

 magnifier; for the wake they made in swimming to and fro was very 

 visible, though the body that made it was not so. Now, if I could see 

 the wake of an invisible animalcule, I imagine I might much more easily 

 see its light if it were of the luminous kind. For how small is the extent 

 of a ship's wake, compared with that of the light of her lantern. 



^" Possibly at Stratford, Conn., where, during the summer of 1750, Franklin visited 

 Samuel Johnson, an Episcopalian minister and later the first president of King's Col- 

 lege, now Columbia University, (from C. Van Doren, Benjamin Franklin, 193, 1938) . 

 It is unlikely that Noctiluca was among the organisms observed by Franklin. Franklin 

 left for England in 1757. 



^' A. H. Smyth, The writing of Benjamin Franklin 3: 192, New York and London, 

 Macmillan, 1905. 



