Electroluminescence 273 



New matter of the first element must keep coming from the mercury 

 to make the light visible and hence the light only lasts while the 

 mercury descends. 



Repetition of Bernoulli's new methods by the French Academy 

 also gave trouble, but in September, 1706, M. Du Tal, in an article 

 published in the Nouvelles de la Republic des Lettres in 1716 con- 

 firmed Bernoulli's results using well purified mercury, and suggested 

 that the Academy members had not carried out his directions exactly. 

 This was undoubtedly true, for Bernoulli's reasoning and experi- 

 ments were all that could be desired. It is probable that the reason 

 some barometers did not luminesce was the presence of quenchers 

 as impurities and the experiments may be taken as the first to 

 demonstrate quenching of electroluminescence, but it is difficult to 

 assign a name to the discovery. 



However, Bernoulli's chief claim to luminescence fame lies not 

 in his barometer experiments but in demonstrations which followed 

 from them, described in his second letter to the French Academy, 

 November 6, 1700. He placed clean mercury in a clean phial well 

 exhausted of air and found that a brilliant light appeared whenever 

 he shook the phial. This was called the " perpetual phosphorus," 

 which would last forever. Bernoulli wrote: " The curious to whom 

 I have shown them [the exhausted phials containing mercury] have 

 declared, that they have seen nothing more wonderful, in short, the 

 whole phial is in a flame, and the quicksilver like a burning liquor." 



When air was let in, the light no longer appeared on shaking and 

 the mercury surface was found to be covered with a pellicle. In a 

 third letter, July 5, 1701, Bernoulli described preparing some par- 

 ticularly pure mercury, which he placed in a scrupulously clean 

 phial and found that it gave light by shaking when the vial was 

 full of air. The light 



appeared only like separate sparks, which arose successively and perished 

 almost at the same time; whereas the light in the vacuinn is like a con- 

 tinual flame which lasts incessantly while the quicksilver is in agitation. 

 I conclude from these experiments, that the quicksilver, if it be per- 

 fectly purified, may let the subtile matter (which I call with M. Descartes, 

 by the name of the first element) go out of its pores in such a quantity 

 at once, that for all the resistance of the air, it has still motion enough 

 to produce some light. 



The visual evidence for an electrical origin of the light was thus 

 described by Bernoulli, but at that time electrical knowledge was 

 confined to attraction and repulsion, with no inkling of the spec- 

 tacular development to come. 



The experiments of Bernoulli aroused the interest of the English 



