British Association for the Advancement of Science. 307 



since the iron bar became by induction a stronger magnet than the 

 steel, and hence the mutual actions of the iron bar and the magnets 

 was more powerful. 



The very limited space within which magnetic action is confined 

 presents a very considerable obstacle. The power is inversely as 

 the square of the distance ; at the eighth of an inch the power even 

 of a large magnet is comparatively trifling. The stroke of one eighth 

 of an inch, directly applied to machinery, would be nothing : we must 

 increase the stroke, and at the same time diminish the power as little 

 as possible. If we increase the stroke, by increasing the distance 

 between the bar and the magnets, we diminish the power inversely 

 as the square of the distance ; if by applying the power of the mag- 

 net at the shorter arm of a lever, we diminish only in the inverse 

 ratio of the distance : thus, if it is wanted to increase the stroke 

 twelve times, the power in one case with the smaller distance, is to 

 the power in the other with the larger distance, as the square of 

 the larger is to the square of the smaller, as 12 2 : l 2 : : 144 : 1. 

 With a lever, the power with the smaller distance is to the power 

 with the larger as the distance in the latter case is to the distance 

 in the former, : : 12:1. The power in any case is much diminished ; 

 but as we can create it in any quantity, this is of little consequence. 

 The repulsion of the magnet for the bar, though considerable, is 

 much less than its attraction. 



The construction of the machine by which Mr. M'Gauley has 

 exemplified the application of magnetism as a moving power is 

 easily conceived. An oaken frame supports two magnets, A and B, 

 horizontally. The bar P K, fixed in a strong pen- 

 pi dulum of wood, of which S is a horizontal section, 



J* * I "N swinging on steel knife-edges, vibrates between the 

 (a Sm B } magnets, and has attached to its lower extremity a 

 V J rod connected with the reversing apparatus and 



any other required machinery. The poles of the 

 magnets are simultaneously reversed, and the bar 

 driven with great force from one to the other, and with a ve- 

 locity of two or three hundred vibrations in a minute. The ap- 

 paratus for reversing the poles is simple, and can be adapted almost 

 without increasing its weight to any combination of magnets. Let 

 A 13 represent the axis upon which the wires w w and 



K 



w' w\ crossing each other under it, are turned ; these clip into 

 cups of mercury, c and c', connected with each other by the 



2 R 2 



