10 



Prof. A. Battelli and Mr. L. Magri 



•i on 



Vicr. 2. 



9. The spark to be photographed was produced in A (fig. 3) 

 within a large wooden box, intercepting any irradiation of 

 light by the spark. 



This box, C, had a hole capable o£ being opened and 

 closed by means of an ordinary pneumatic shutter, as used 

 in photography. 



A card-paper tube reaching as far as the objective L (an 

 astigmatic Zeiss objective) projected from 0. The image 

 formed by L was reflected, by the rotating mirror S on to the 

 photographic plate F, if the mirror was in the proper position. 



