HAUKSBEE'S LUMINOUS FOUNTAIN. 



459 



kindred to the amber light or cat's-back light, than to the 

 light due to the striking of flint and steel. In fact, as will 

 be apparent further on, his impressions evidently were that 

 the last-named alliance was the most probable. 



The question which had been most debated bore upon 

 the need of a vacuum existing in the vessel which con- 

 tained the mercury, and to that he first directs attention. 

 He proves almost immediately that, by allowing air to 

 rush through quicksilver in an ex- 

 hausted receiver, he can convert 

 the liquid metal into a jet dash- 

 ing in drops in every direction 

 against the sides of the vessel, and 

 looking, as he says, u like one 

 Great Flaming Masse." Then he 

 permits mercury to flow downward 

 into an exhausted receiver so as 

 to strike a rounded glass surface 

 therein and so become spread. A 

 shower of fire appears; luminous, 

 however, only (his observation is 

 very quick) "where it strikes the 

 glass in its fall." Now he lets in 

 three pounds of mercury at once 

 in a cascade, and then u the light 

 darted thick from the crown of the 

 included Glass like Flashes of 

 Lightning." 



They were flashes of lightning, 



and this was the first suggestion of that great identity by 

 one who was building far better than he ever knew. 



The behavior of the light is curious. When the mer- 

 cury falls into a vacuum, there is a gentle, uniform glow; 

 but when it pours into air, the sparks dance between 

 the glistening drops. What are the sparks? Certainly, 



1 Reproduced in fac simile from s'Gravesande's Elements of Natural 

 Philosophy. 4th ed. 1731. 



HAUKSBEE'S LUMINOUS 

 MERCURIAL FOUNTAIN. 1 



