Polytechnic Association. 595 



of two concentric wheels, united together at a point about equi-distant 

 between the rim and the hub, by elastic packing, which takes the jar 

 from the imperfections of the track before it reaches the axle. The 

 outer part of the wheel is chilled iron, and the center is soft iron. 

 The mechanism is very simple, and adapted to preserve the car from 

 jar, and the axle from breaking. 



The President — We had before us last year an elastic wheel, 

 intended to accomplish the same end as this. 



Mr. J. K. Fisher. — Have there been any experiments to determine 

 the force of traction required for this wheel ? 



Mr. Partridge — I do not know that there have been any experi- 

 ments ; but the theory is that it requires the same force as if the 

 whole interior were of the same substance with the packing. The 

 extra traction, I take it, is just equal to the friction in the spring. 



The President — I do not think there is much loss there. 



Mr. Fisher — The assumption is that the elasticity of the spring 

 is perfect. I question that perfect elasticity ; and I think we need 

 the practical test. 



Electricity as a Motive Power. 



Dr. L. Bradle resumed the discussion of the subject of the use of 

 electricity as a motive power. 



He exhibited a model of a new electro-magnetic motor, made with 

 two pairs of magnets. When the circuit is closed for one magnet of 

 a pair, it is broken for the other. The dead center of one pair of 

 magnets corresponds with the half stroke of the other. He had 

 never been able to recognize the law stated by Professors Phin and 

 Yan der Weyde, that the resistance of the coil and the resistance of 

 the battery should be equal. He considered the results by this motor 

 as contradicting that law. He was satisfied that he had obtained 

 altogether better results by putting a good deal more resistance in the 

 magnet than there was in the battery. He was satisfied, also, 

 that inserting an iron core in a spool did not increase the resistance ; 

 and he illustrated these several points by experiments. He also 

 exhibited and explained his tangent galvanometer. 



Dr. Van der Weyde — A great deal depends on the relation of the 

 size of the wire to the strength of the battery. Again, much depends on 

 the character of the coil. The first layer has more effect, being closer 

 to the iron. Additional windings increase the power, but to a less 

 extent ; until finally we reach a point where the windings are so far 



