96 History of Luminescence 



quality in " the transparent " (Aristotle) . These views were dis- 

 cussed over the succeeding ages and were still a matter of argument 

 in the early seventeenth century. 



About the time of Descartes' greatest activity, the famous confer- 

 ences ^^ of Theophraste Renaudot (1586-1653) were being held at 

 the Bureau d'Addresse in Paris. They give an excellent idea of 

 contemporary opinion. In one of these conferences, on January 2, 

 1635, six opinions on the nature of light were expressed, and lumi- 

 nescences were used to support two of these opinions. It was argued 

 that light is a form connected with rarity or transparence (the view 

 of Aristotle) by the fact that 



we find light in sundry animated bodies, as in the Eyes of Cats, and of 

 those Indian Snailes [perhaps Pyrophorus] which shine like torches, and 

 in our Gloe-worms, whose light proceeds from their Spirits; which being 

 a middle nature between the Body and the Soul, are the least material 

 thing in the world. . . . Whence it follows that Light is a form with the 

 most of essence among sensible formes, as obscurity hath the least. 



Another opinion, that of the Florentine philosopher, Marsiglio 

 Ficino (1433-1499) , held that rarity alone could not be a cause of 

 light, since the fact that 



burning mirrors made of steel, the hardest of all metals . . . make the 

 Sun-beams do more than their own nature empowers them to, shews 

 sufficiently that their Light cannot arise from a rare and diaphanous 

 cause. Nor may the light of rotten wood be assign'd to its rarity alone, 

 since many other bodies of greater rarity shine not at all; nor that of 

 Gloe-worms and Cats-eyes to their spirits, since the flesh of some animals 

 shines after their death; as 'tis affirm'd of Oxen, that have frequently 

 eaten a sort of Moon-wort; and not onely the scales of divers fishes shine 

 after separation from their bodies, but sparkles of fire issue from the 

 hair of some persons in great droughts, whereunto the spirits contribute 

 nothing. 



Such were the arguments in 1635. 



Descartes' views on light were announced in his Discours de la 

 Methode . . . plus la Dioptrique, les Meteores et la Geometrie, pub- 

 lished anonymously at Leyden in 1637 as Essais Philosophiques. The 

 Meditations appeared in 1641. The theory was amplified in the 

 Principia Philosophiae (Amsterdam, 1644) , which contains his ideas 

 on the constitution of matter and the universe. Briefly, Descartes 



^* These were talks over the years 1633-1642 on matters of social and scientific 

 interest, published as Feuilles du Bureau d'Addresse (Paris, 1636) with an English 

 translation by G. Havers, Gent., A general collection of discourses of the virtuosi of 

 France, upon questions of all sorts of philosophy, and other natural knowledge, 1664. 

 The quotations are from this book. 



