in Magnetic Circuits. 323 



planes. No externally applied mechanical force was used to 

 force the surfaces together. 



Table I. 



Influence of a smooth joint in an iron bar. 



Magnetizing Force 

 due to solenoid. 



Magnetic Induction 93. 



Without joint. 



With joint. 



4 



3950 



3000 



6 



6900 



5300 



8 



9250 



7400 



10 



10900 



9150 



15 



13250 



12000 



20 



14300 



13500 



30 



15200 



14900 



In fig. 1 these results are shown by curves, and a third 

 curve (the dotted line) is added to show the values of «£>' — «£) 

 in terms of 53. It will be seen that this curve is nearly a 

 straight line ; it should be straight if the magnetic resistance 

 of the joint were strictly constant. Table II. gives values of 

 the width of air-gap equivalent in magnetic resistance to the 

 joint, as determined from this experiment. 



Table II. 



33. 



Width of air-gap equivalent 

 to the joint, in centimetres. 



4000 



00026 



6000 



00030 



8000 



00031 



10000 



00031 



12000 



0-0035 



14000 



00037 



Data relating to a second experiment in which a cut with 

 true-plane surfaces was introduced in another iron bar will 

 be found in the former paper. Fig. 2 shows the graphic 

 treatment of this example, and it will be seen that the dotted 

 curve which exhibits »£)'— <$ is in this case slightly concave 

 towards the axis of 23, whereas in the former example it was 



