122 Duration of Flash of Exploding Oxyhydrogen. 



In some cases the luminous gas in the photograph was 

 confined within the walls of the bulb, while in other cases a 

 cloud or outburst was noticed at some particular spot outside 

 the wall. The image of the pendulum wire in one case came 

 in front of this cloud and was found to be much more blurred 

 than the pin, indicating that the light of one of these out- 

 bursts lasts longer than that of the mixture within. This 

 may be due to an admixture of outside air, which increases 

 the time of combustion. 



I find that the light of these exploding bulbs is quite suit- 

 able for photographing small objects in rapid motion such as 

 water-jets ; and in some cases may be preferable to the spark, 

 the electrostatic strain just before the flash tending to deform 

 the jet. In one of the photographs, where an outburst has 

 taken place directly against the jet, there are curved traces 

 around the drops, apparently where the burning gases are 

 rushing around them. 



For the purpose of photographing jets, I think that a better 

 device than the thin bulb would be a shallow, rectangular tin 

 tray with a highly polished bottom, such as a box cover. 

 This could be covered with a thin film of mica fastened on 

 with wax, and the vessel filled through two small tubes. The 

 reflecting back would increase the amount of light without 

 increasing the depth of the exploding layer, which of course 

 tends to prolong the flash. 



Note. — On receiving the proof of the above paper I was 

 much surprised to find that the photograph, which I had 

 enclosed as a curiosity with the MS., had been reproduced. 

 I had no idea that the picture would be considered of interest 

 enough to warrant reproduction, or I should have taken 

 pains to secure a better one. My best negative came to 

 grief, and the picture reproduced is the first attempt at 

 securing a water-jet by the flash, taken merely to ascertain 

 whether the method was feasible. Much of the detail has 

 been lost in reproduction, but the upper parts of the jet show 

 well. No especial pains were taken to secure uniform jets, 

 though the right-hand one is fairly good. An oblate spheroid, 

 on the end of a liquid thread, then a chain of fine little drops, 

 formed by the breaking up of a thread, then the prolate 

 spheroid. 



The outbursts of gas show fairly well in this photograph, 

 and at the bottom of the left-hand jet two blurred drops are 

 dimly seen, showing the longer duration of this part of the 

 flash.— R. W. W. 



