ELECTRIC-SPARK PHOTOGRAPHS. 167 



and absolutely at rest and clear, and if it were not that I could at once 

 illuminate it by ordinary liglit it would be difficult to believe tliat it was 

 still in motion. 



The electric spark lias been often used to produce a flasli by means 

 of which phenomena have been observed which we ordinarily can not 

 see. For instance, Mr. Worthington has in this way seen and drawn 

 the exact form of the splash produced by a falling drop of liquid. 



Mr. Chichester Bell, Lord Eayleigh, Mr. F.J. Smith, and others have 

 used the illumination produced by an electric spark to photograph 

 ph«'nomena which they Avere investigating. I am able to show one of 

 Lord Eayleigh's, a breaking soap bubble, in which the retreating 

 edge, travelling something like 30 miles an hour, is seen with all the 

 accuracy and sharpness that is possible with a stationary object. Mr. 

 F. J. Smith has extended the use of sparks for the purpose of physi- 

 ological inquiry, taking a row of photographs on a moving plate at 

 intervals that can be arranged to suit the subject, and is thus putting 

 in the hands of the much-abused experimental physiologist a very pow- 

 erful weapon of research. I had hoped to show oue of these series of 

 an untechnical character, to wit, a series taken of a cat held by its four 

 legs in an inverted position and allowed to drop. The cat, as every 

 one is aware, seems to do that which is known to be dynamically 

 impossible, namely, on being dropped ui:>side down to turn round after 

 being let go and to come down the right way up. The process can be 

 followed by means of one of Mr. Smith's multiple spark photographs. 

 However, his cats do not seem to like the experiments, and he has in 

 consequence had so much trouble with them that his results, while 

 they are of interest, are not, up to the present, suitable for exhibition. 



Let me now return to single spark photographs. We have seen that 

 the magnesium flash, which for the purpose of portraiture is practically 

 instantaneous, yet fails to appear so when so moderate a speed as 40 

 miles an hour (iind indeed a far lower S|)e<'d) is used for the purpose of 

 examining it. Is anything of the kind true in the case of the electric 

 spark ? Will the spark, by which we saw the clock-face absolutely 

 sharp, after all fail to give a sharp view when tested by a much higher 

 speed? 1 have taken such a spark and attempted (though I knew 

 what the result would be) to photograph by its light the l)nllet of a 

 magazine rifle passing by at the rate of about 2,100 feet a second, or, 

 Avhat is the same thing, at about 1,400 miles an hour; the result (PI. ii, 

 fig. 3) shows not a clear, sharp bullet, but a blur; the spark lasted so 

 long a time that this bullet was actually able to travel half an inch or 

 so while the illumination lasted. Thus Ave see, that if we wish to exam- 

 ine bullets, etc., in their flight, any electric spark will not necessarily 

 do. We shall have to get a spark which while it gives enough light to 

 act on the plate yet lasts so short a time that even a rifle bullet can 

 not move an ax^preciable distance during the time that it is in exist- 

 ence. 



