upon the Dimensions of Iron and Steel Bars. 



231 



this place, that the oreater proximity of the magnetic balance 

 to the coil increased the numbers in columns 5, representing 

 the magnetic intensity of the six-inch pillars. The two pre- 

 ceding tables are therefore only comparable with themselves. 

 In all the other experiments with one-foot bars, the magnetic 

 balance was at the uniform distance of 4t inches from the 

 centre of the bar, so that they are strictly comparable with 

 one another. 



I now proceed to give an account of some experiments on 

 the effects of the force of tension. The bar employed was a 

 piece of soft iron wire 12f inches long and a quarter of an inch 

 in diameter. Its extremities were formed into very fine- 

 threaded screws, extending one-third of an inch, for the pur- 

 pose of screwing into the brass plate and bolt, as shown in the 

 figure already described. The effectual length of the bar, 

 when screwed into its place, was exactly one foot. In the 

 first experiment of this kind, the tension employed, being that 

 occasioned by the weight of the lever alone, amounted to 

 80 lbs. In the subsequent ones the tension was further in- 

 creased byplacing weights on the lever. 



Experiment 13. Iron wire one foot long and a quarter of 

 an inch in diameter. Tension 80 lbs. 



