Flash of Exploding Oxyliydrogen, 



121 



to give an image of natural size in order to simplify the 

 measurements. 



With a velocity of 3 metres a second the image of the 

 round pinhead was as sharp as if stationary ; but on raising 

 the pendulum to a height sufficient to give it a velocity of 

 6 metres a second, a blur amounting to a trifle less than 

 •5 millim. was observed. The pendulum -point moving 6000 

 millim. in a second would traverse a distance of *5 millim. in 

 the ^ of a second, consequently the duration of the flash is 

 somewhat less than j^— ■ sec, probably about ■ * sec. 



Of course the total duration of the flash depends on the 

 speed of propagation of the explosion in the mixture, as well 

 as on the actual duration of the flash of each exploding 

 element ; Le Chatelier found that this velocity was about 

 1000 metres a second. 



The bulbs being about 8 centim. in diameter, and the point 

 of ignition in the centre, the explosion would reach the walls 

 in 2 5ooo of a seco »d. This being about one half of the total 

 duration, we may suppose it to be about the duration of the 

 flash of any small element. 



