490 



Mr. S. Bidwell. On the Lifting Power* of [June 10, 



circuit with the coil by depressing a key, the rod carrying the scale- 

 pan was introduced into the coil and held in contact with the fixed 

 rod. Weights were then placed in the scale-pan and the key momen- 

 tarily depressed, the lower rod at the same time being left free to hang 

 or to drop ; and this operation was repeated with various weights in 

 multiples of 10 grams until it was found that the further addition of 

 10 grams was sufficient to detach the two rods from each other. A 

 record having been made of the greatest weight which was supported, 

 the current was switched through the German silver wire and a 

 galvanometer reading was made with the current both direct and 

 reversed. The same process was gone through with currents of 

 different strength until the whole number of 27 battery cells had been 

 used. 



The results of the experiment are given in Table I, the first column 

 of which shows the intensity of the magnetic field at the centre of 

 the coil, and the second the weight supported per square centimetre 

 of the section of the rod. In fig. 1 the weight supported has been 

 plotted against the intensity of the field, and it will be seen that the 

 curve from || = 270 upwards, is, within the limits of experimental 

 error, a perfectly straight line, which is represented by the equation 

 W= 516 1 + 9563. 



Table I. 



Divided rod. 



Divided ring. 



Magnetic 



Weight 



Magnetic 



Weight 



force. 



supported. 



force. 



supported. 



C.G-.S. units. 



Grams. 



C.G-.S. units. 



Grams. 



40 



6,550 



3 9 



2,210 



67 



7,640 



5-7 



3,460 

 5,400 



163 



9,460 



10 3 



264 



10,920 



17-7 



7,530 



404 



11,650 



22-2 



8,440 



616 



12,920 



30-2 



9,215 



735 



13,290 



40 



9,680 



896 



14,010 



78 



11,550 

 12,170 



1010 



14,740 



115 



1074 



15,110 



145 



12,800 





208 

 293 

 362 

 427 

 465 

 503 

 557 

 585 



13,810 

 14,350 

 14,740 

 15,130 

 15,275 

 15,365 

 15,600 

 15,905. 



