Polytechnic Association. 587 



Prevost, asserted that the power of a battery could be increased by 

 adding magnets. The fact is, that so long as the resistance in the 

 coil is less than the resistance in the battery, you can increase the 

 power until you make them equal. But many who make such 

 machines do not know how to calculate the resistance. In the first 

 place, it is in inverse ratio to the section of the wire. Then there is 

 another principle. If you have two wires, and if the resistance in 

 one is 100 times that in the other, the current will not all go in the 

 easiest way, but one-hundredth part of it will go the other way ; 

 or rather, 100 times as much will go the easiest way as goes the 

 other way. 



Mr. T. D. Stetson — What will be the effect if the magnet does work ? 



Dr. Yan der "VVeyde — It will affect it by interrupting the current. 

 The magnetization and demagnetization of the iron will interfere 

 with the primary current and diminish, it. In other words, it will 

 increase the resistance. 



Dr. L. Bradley — What will be the effect of the armature ? 



Dr. Van der Weyde — When loaded with an armature the resist- 

 ance will not be changed ; but when they are not loaded, so that the 

 magnetism is fuee to manifest itself, the resistance will be increased. 

 Taking off the armature will increase the resistance. 



The President — The gain in multiplying these magnets is like the 

 gain by a lever. It is only a gain in the manner of using the power. 



Adjourned. 



May 25, 1872. 



Prof. S. D. Tillman in the chair; Mr. Robert "Weir, Secretary. 



The President, Prof. S. D. Tillman, read the following summary 

 of scientific news : 



I. ]STew Coal Mines in India. 



The London Mining Journal contains some interesting statistics 

 with reference to the newly-discovered coal mines of Berar, in India. 

 The total area of the coal-fields is more than 1,000 square miles, and 

 the coal is easily accessible. Lately, a vein of coal was struck seventy- 

 seven feet from the surface, and thirty feet of coal was pierced without 

 the bottom of the seam being reached. The area of one field, called 

 the Damuda, is estimated at 110 square miles, and the average thick- 

 ness of the vein at forty feet. Valuable beds of iron ore have also 



