ACCUMULATORS. 361 



"We will now proceed to examine some of these springs in 

 detail. 



THERE is one form of elastic spring which has of late years 

 become more familiar than agreeable, namely, the toy which is 

 learnedly called a " catapult," though it has little in common 

 with the ancient weapon whose name it bears. 



As may be seen by reference to the illustration, it consists 

 of one or more india-rubber straps attached to a fork-like 

 handle, and carrying a small pouch in which is contained the 

 missile. Although it is not remarkable for accuracy, it can 

 throw a stone or a bullet a considerable distance, and its power 

 can be very quickly increased by adding to the number of the 

 straps. Thus a catapult has been made which was capable of 

 sending a small pistol bullet through a wooden board, so that 

 the child's toy might really become a dangerous weapon. 



Indeed, cases are known where the catapult has hurled a 

 stone with fatal effect upon human beings. In my own neigh- 

 bourhood there are many examples of glass being pierced by 

 stones thrown from catapults just as if they had been subjected 

 to bullets shot from firearms, the holes being quite small and 

 round. 



The power of accumulating force by increasing the number 

 of springs was utilised by Mr. Scaife, when he invented his 

 wonderful photographic machine which he termed the " Pisto- 

 lograph," on account of the sound which was produced when 

 the portrait was taken. 



The idea was simple enough, though the practice of it was not 

 so easy. He wished to be able to take a photograph with an 

 exposure of the least possible time, and thus to attain freedom 

 and action, instead of the dull stiffness which generally charac- 

 terizes photograph portraits. The mode which he adopted was 

 by introducing a peculiarly sensitive film, which would take 

 an impression in a mere moment, and then arranging the 

 machine so that an exposure of more than a moment was 

 impossible. 



This was done by covering the lens with an exactly fitting 

 door, revolving on a pivot. The axis on which the door 

 revolved was attached to a number of india-rubber bands, 

 exactly like those which are used for confining papers. As the 



