176 Professor William Stirling [May 12, 



31. Bull and Flight of Insects. 



The cinematograph has been applied with conspicuous success to 

 the study of the flight of insects, by M. Lucien Bull, of the Institut 

 Marey, Paris. M. Bull assisted the late Professor Marey with his 

 experiments on this subject. 



Two Tliousand Photograplis per Second. 



When it is remembered that the movements of the wing of the 

 common fly occur at the rate of ?u>0 vibrations per second, the bee 190, 

 the wasp 110, and the dragon fly 28, it will be seen that there are many 

 technical diflBculties to be overcome. M. Bull, by the means of his 

 ingenious "Electro-stereo-chronophotograph," has been able to take 

 photographs of a moving object at the rate of two thousand impres- 

 sions per second on a sensitized film. As is well known, the electric 

 spark — with a duration of one-millionth of a second — affects our 

 singularly sensitive visual apparatus most markedly. Photographs 

 have been often taken by means of a single spark. M. Bull, how- 

 ever, has constructed an apparatus whereby a series of two thousand 

 such impressions can be obtained per second by means of the electric 

 spark. 



In a special camera is placed a revolving wheel, on the circum- 

 ference of which is arranged the sensitized film. The electric spark 

 is placed behind a large condensing lens which concentrates the rays 

 directly into the lens of the camera. The wheel, actuated by an 

 electrical motor, is rotated at a speed of about 150 kilometers per 

 hour, i.e. it makes one revolution in one-fortieth of a second. In 

 circuit is placed the electric illuminant — the sparks passing between 

 two magnesium terminals. The wheel, however, is so arranged as to 

 give fifty interruptions at each revolution, so that in this way two 

 thousand sparks per second are obtained — the duration of each spark 

 being practically infinitesimal — while the intervals between the sparks 

 are practically a thousand times the duration of the sparks themselves. 

 The whole system may be regarded therefore as comparable to a 

 shutter opening and closing two thousand times per second. 



The next problem was how to expose the film at the proper moment. 

 A similar problem was solved in an ingenious way by Helmholtz long 

 ago when he invented his Myograph with a small cylinder, on which 

 he recorded the rate of transmission of a nerve-impulse along the 

 motor nerve of a frog — really a comparatively slow velocity — about 

 ninety feet per second. 



By means of an ingenious shutter the exact exposure was made at 

 the right moment, and this was accomplished indirectly by the insect 

 itself, which was placed in a short length of blackened glass tube 

 closed at one end by means of a light movable mica swing door, 

 which is placed in the electric circuit. The door is kept slightly ajar 



