138 History of Luminescence 



why fire-flies, having been exposed to the sun and then tightly shut in a 

 glass, shine with greater brilliance at night as long as the air which is con- 

 tained in the tubes and bladder of the fire-fly is set into quick vibration 

 by the motion of the sun and is thus preserved. 



A drawing depicting his firefly experiments is reproduced as figure 

 13. 



Bottoni was particularly critical of Kircher, who had stated that 



the nitedulae [fireflies] have obtained this innate light as something 

 intrinsic by the providence of nature in order that they may see and 

 be seen. But how could an ignorant overseer [of an estate] have expressed 

 anything more clumsy? And why should a just nature have endowed 

 these worms with this privilege of light while refusing it to other little 

 animals, thus being liberal towards the first and stingy towards the 

 others? The explanation for this phenomenon is simple because in dif- 

 ficult things we often take refuge in the occult. What eludes the vision 

 of the human mind in the natural world, we try in vain to attribute to 

 mysterious, especially divine, forces. Rather we should explain those 

 phenomena by natural reasons, resorting to the world of senses as much 

 as we can. 



His own explanation of luminescence, that " when there is motion 

 induced, fiery sparks come forth," seemed particularly applicable to 

 sugar and to the light of the sea. Bottoni wrote: 



Sugar, which is rich in fiery particles, when kneaded with more solid 

 substances, emits sparks. In the same way particles of salt from the 

 sea shimmer after they have been deposited when the sea becomes calm 

 again, and they shine forth from the violent motion of the flood beating 

 against the rocks, or breaking after the rising of a storm. When the air 

 has been stirred up into whirlwinds, when the waves are impetuous and 

 excited winds are blowing, it strangely looks as though flames were 

 hanging on the masts of ships [St. Elmo's fire]. 



If we recall how quickly air in motion will rekindle a smouldering 

 fire and produce a bright light, Bottoni's argument does not seem 

 so ridiculous. 



JACQUES ROHAULT 



As pointed out in a previous section, Descartes was mostly con- 

 cerned with the universe and man, practically neglecting lumines- 

 cence, but some of his followers treated the subject in some detail. 



One of these was Jacques Rohault (1620-1675), the eminent 

 French mathematician and physicist of the Cartesian School, who 

 wrote a Traite de Physique^- (1671), which was translated into 



»=See G. Sarton, Isis 38:137-148, 1947-1948, for the various editions of Rohault's 

 famous textbook. 



