276 



Dr. Hare's Electrical Machine, &fc. 



according to the manner in which the 

 balls are associated with the positive 

 or negative poles of the machine. 

 When the small ball is attached to 

 the positive pole, the spark is long, 

 comparatively narrow, and of a zig- 

 zag shape, such as lightning is often 

 seen to assume ; but when the situa- 

 tion of the balls is reversed, the spark 

 is straight and thick, not one third as 

 long, and nothing of a zigzag shape 

 can be observed in it. 



According to the Franklinian the- 

 ory, when any body is more highly 

 charged with electricity than the ad- 

 joining bodies, the excess of the fluid 

 is attracted by them, white it is inad- 

 equately repelled by the inferior quan- 

 tity of the electric fluid, with which 

 they are imbued. It follows that when 

 a small globe is made positive in the 

 neighborhood of a large one, the ex- 

 cess of electric matter in the former, 

 is attracted by all the negatively ex- 

 cited metal in the latter. When the small globe is made negative 

 the metal of which it consists attracts all the electric matter in the 

 large globe. Hence there is this difference in the two cases ; the 

 small globe being positive, a comparatively small movable mass of 

 electric matter, is attracted by a large immovable mass of metal : the 

 small globe being made negative, a large movable mass of electric 

 matter is attracted by a small immovable mass of metal. The charge 

 being in both cases the effect of the same machine ; the attractive 

 power must be as great in one case as in the other. The forces by 

 which the masses are actuated being therefore equal, it is quite rea- 

 sonable that the greatest projectile power should be attained, when 

 the small mass is movable. In that case, it will require less air to be 

 removed in order to effect a passage. 



There is an analogy between the difference which I suppose to 

 exist in the case under consideration, and that which maybe observ- 

 ed between the penetrating power of a rod which is blunt, and one 

 which is pointed. 



