The Eighteenth Century 151 



attraction and repulsion, a dissection of the eye, and the working 

 of microscopes and telescopes, there were to be shown—" Tlie Elec- 

 trical Phosphorus, The Mercurial Phosphorus, The Liquid Phos- 

 phorus, The Solid Phosphorus, and The Light of Phosphorus 

 augmented in Vacuo.'' 



Prize Essays 



It has been pointed out that when the first societies were formed 

 in the seventeenth century, the custom was to carry out experiments 

 at the meetings. The Royal Society allotted particular inquiries to 

 members or groups of members who were to report on them after 

 special study. At the beginning of the eighteenth century a change 

 occurred. Prizes were bestowed for the solution of general problems, 

 treated in the form of an essay. 



JEAN JACQUES DORTOUS DE MAIRAN 



One of the first of these prizes was offered in the field of lumi- 

 nescence by the Bordeaux Academy of Science, established in 1703. 

 It was won by de Mairan (1678-1771) , later a member of the French 

 Academy, physicist and mathematician, who succeeded Fontenelle 

 as perpetual secretary in Paris. His essay - was entitled Dissertation 

 sur la Cause de la Lumiere des Phosphores et des Noctiluques, a 

 54-page booklet, published at Paris in 1715 and at Bordeaux in 1717. 

 The title page is reproduced as figure 15. The preface stated that 

 this was the third prize won by de Mairan and added new glory to 

 his triumphs. Later he was to become famous as the creator of a 

 new theory of the aurora borealis (see Chapter VII) . 



De Mairan's prize essay is of particular interest because it gives 

 an excellent insight into the explanations current at the beginning 

 of the eighteenth century. The first twenty-four pages were devoted 

 to a discussion of the two theories of light— that it consisted either 

 of waves propagated in the ether or was an effusion of corpuscles. 

 De Mairan upheld the latter view. He believed that the light sub- 

 stance (matiere lumineuse) consisted of sulphur, " very subtile and 

 very restless (agite) . It alone of the five principles (sulphur, salt, 

 earth, water, and mercury) known to chemists has the property of 

 acting on and transmitting its action to other substances." De Mairan 

 stated that the words " Phosphores " and " Noctiluques " would be 

 used synonomously. He divided them into the natural and the 

 artificial. 



The natural phosphores were glowworms, flies, caterpillars, other 



''A disappointing work, according to both Heinrich (1815) and Ehrenberg (1834). 



