Lifting Power of the Electro-Magnet. 



519 



inches of whose cylinders are iron, the rest brass. "When the hehces were on 

 the brass, just below the iron, the lift was but Q-IS of its amount when they 

 were on the iron. At the extremity of the hehx, the exciting force might be 

 supposed to be little less than in its interior. The constants of the helices 

 which I used are 



( G), (H), and (/) are from Mr. Bergin's collection ; the two last were 

 kept concentric with the magnet by wooden framing, though a considerable 

 error in this respect seems to have little eifect. 



The results obtained with (S) are given in a separate Table, as they were 

 intended to be used for interpolation beyond the range of Table viii., and. 

 therefore, the first diiferences are included in it. L' is reduced by (13), the 

 cylinders being 21. 



