Lifting Power of the Electro-Magnet. 



517 



through the section of the wire. The error, however, must be trifling. Their 



L is reduced by (12), as from the shortness of the cylinders it must nearly be 

 exact for them also. These results are in a ratio so different from what I anti- 

 cipated, that I suspected some error was produced by the overlapping of the 

 spirals E. I therefore repeated the experiments with one of Mr. Bergin's 

 magnets, in which the distance of the axes is 7-5, and the length of the cylin- 

 der 0'-5 ; but it gave similarly 



Both sets agree in showing that the power of a spire does not decrease nearly 

 so fast by an increase of diameter as the equation (7) assigns. In both the yu 

 is diminished relatively to that of A by the greater length of the cylinder, and 

 (in the second) of the entire magnet and its keeper, as will be more evidently 

 shown hereafter. As, however, {D) ia almost identical in its diameter with A, 

 by taking it as unit, we get a more distinct comparison of the relative values of ^. 



3x2 



