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 “Pistolograph,” 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 characterizes 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 power of the springs increased with their number, it naturally followed that the rapidity of the revolution was in exact ratio with the number of the bands, so that the duration of exposure to light could be measured with tolerable accuracy. So wonderfully well did this plan succeed that photographs of eclipses were taken with perfect accuracy, a matter of great importance when time has to be considered. Horses were also taken at full gallop, so as to display their action, and the crowning achievement was the photographing of a cannon in the act of firing, and the bursting of a charged shell. So rapid is the action of the instrument, that in several cases where a cannon or mortar had been photographed, even the track of the ball or shell is visible. [Illustration: LEAF-ROLLING NESTS.] [Illustration: CATAPULT.] It necessarily followed that when the springs caused the circular cover to revolve with such rapidity, they made it close with a sharp report, and so gave rise to the name of the machine. Moreover, as it had to be used for rapidly moving objects, it was not fixed on a pedestal, but was held in the hands, while aim was taken at the object, just as with a pistol. When the observer thought that he had his aim correct, he touched a trigger, round spun the cover, and the photograph was taken. * * * * * ON the right hand of the illustration is seen the Catapult, made with several springs, and on the left is shown an example of the Accumulator as formed by Nature.