ELECTRIC-SPARK PHOTOGRAPHS OF FLYING BULLETS.* 



By C. V. Boys, F. R. S. 



When I was honored by the iuvitatiou to deliver this lecture I felt 

 some doubt as to my ability to tiud a subject which should be suitable, 

 for there is a prevailing idea that, in addressing- the operative classes, 

 it is necessary to speak only of some practical subject which bears 

 immediately npou the most important industry of the place in which 

 the lecture is being delivered ; but it seems to me that this is a polite 

 suggestion that the audience are unable to be interested by any subject 

 except that particular one which occupies them daily. Now, though I 

 am a comparative stranger in Scotland, I have heard quite enough and 

 I know quite enough, of the superiority of the education of yon, who 

 have the good fortune to live in this the most beautiful half of Great 

 Britain, to be aw^are that, as is the case with all highly educated men, 

 you are able to take a keen and genuine interest in many subjects, and 

 that I had better choose one to which I have specially devoted myself, 

 if I do not wish to expose myself to the risk of being corrected. I 

 will ask you therefore in imagination, to leave your daily occupation 

 and come with me into the i)hysical laboratory, where, by the exercise 

 of the art of the experimentalist, problems which might seem to be 

 impossible are continually being solved. I wish as an experimentalist 

 to present to yon an example of experimental inquiry. 



Let us suppose that for some reason we wish to examine carefully and 

 accurately some moving object travelling, if you will, at so great a 

 speed tliat, observed in the ordinary way, it appears as a mere blur, or 

 X)erhaps at a speed so tremendous that it can not be seen at all. In 

 such a case, in order to get a clear view of the moving body we may 

 either look through an aperture which is only opened for a moment as 

 the body passes by, or we may suddenly illuminate the object by a 

 flash of light when it is in a i)Osition in which it may be seen. If in 

 either of these cases the hole is 0[)en, or the illumination lasts so short 

 a time that the object has no time to move appreciably while it is in 



* Lecture flelivered at the Edinburgh meeting of tlie British Association for the 

 Advancement Science, August. 1842. (From Nature, March 2 and 9, 1893, vol. XLvn, 

 pp. 415-421, 440-446.) 



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