THE BOOK OF THE LANTERN. 175 



manner. The importance of this experiment, as a demon- 

 stration, will be acknowledged when it is remembered that 

 this movement of a frog's legs, accidentally brought about 

 by Galvani, laid the foundation of our present knowledge of 

 current Electricity or Galvanism, as it used to be called, 

 after that first experimenter. 



Another most effective experiment was shown in con- 

 nection with a lecture upon the Suez Canal by Professor 

 Pepper. After exhibiting a number of experiments upon 

 sand, and showing that it always fell at a certain angle, 

 and exerted lateral instead of perpendicular pressure, 

 an image of an ordinary hour-glass was cast upon the 

 screen. This sand-glass was supported in a frame, and its 

 sides were flattened so that it could fit the lantern stage. It 

 had rather an amusing appearance, because like all instru- 

 ments placed in the lantern, the image was inverted, and 

 the sand therefore appeared to flow upward instead of 

 downward. A curious fact, too, was noticed when this 

 familiar instrument was magnified to such an enormous ex- 

 tent, each particle of sand was seen to strike a blow upon 

 the top of the cone above, and the force from that blow 

 passed from the point of the inverted cone to its base, and 

 formed a peculiar wave -like figure in its passage. 



I have never seen this experiment repeated elsewhere, 

 but it is one that should not be forgotten. 



Among the experiments which can be performed by 

 means of a lantern, and better performed, so far as an 

 audience is concerned, than by any other means, are 

 those relating to cohesion figures. Professor Tomlinson 

 was the first to give much attention to these interesting 



