362 NATURE'S TEACHINGS. 



power of the springs increased with their numoer, 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. 



It necessarily followed that when the springs caused the 

 circular cover to revolve with such rapidity, they made it close 



LEAF-ROLLING XESTS. 



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. 



The reader may probably be acquainted with the Leaf- 

 rolling Caterpillars, of which there are so many. I had often 

 inspected these curled leaves, and, on comparing them with the 



