Polytechnic Association Proceedings. 989 



days. It can be stopped at any time, by laying a wire, or other 

 metallic connection across the rails, and started by removing the 

 same. By this means its movements can be controlled, in the most 

 perfect manner from any part of the hall. 



' The engine is built on a scale of one inch to the foot, the train 

 beius: about five feet in length. The circuit of the hall is somewhat 

 less than three hundred feet, and the maximum speed which the 

 engine has attained is about six feet per second. 



The weight of the engine is eighteen pounds; that of the train 

 about twelve pounds, and it is capable of carrying a maximum 

 burden of fifty pounds, making a total of nearly eighty pounds. 

 It is driven by a battery of seven .Grove's cups; and the working 

 expenses are about one dollar and fifty cents per week. 



The superior efiiciency of this machine is doubtless due, first, to 

 the employment of a great number of small magnets, instead of a 

 few large magnets; second, to the passage of the electric fluid 

 through a great number of short circuits, instead of one long cir- 

 cuit; third, the proximity of the attracting parts, the armatures 

 makino; a o-reat number of short strokes instead of a few lono; 

 strokes; fourth, the equalization of the attractive force of the mag- 

 net; fifth, dispensing with the crank movement, and causing the 

 magnets to act nearly all the time; sixth, the novel arrangement 

 of the current breaker, by which the electric fluid is enabled to 

 pass rapidly and freely through the machine. 



MAGNETISM. 



Prof. Vanderweyde then addressed the Association upon mineral 

 magnetism. Dr. V. reviewed briefly the history of magnetism from 

 its earliest discovery to the present, and made some interesting 

 experiments. He showed that north poles repel each other, and 

 south poles do the same, but north poles attract south poles, and 

 vice versa. He also explained how steel can be magnetized by 

 means of the magnetism of the earth, without a magnet. The 

 Doctor also explained that the magnetic point of the earth lies 

 somewhere on the northern part of this continent, nearly on a line 

 with the Mississippi; but the precise point is not yet determined. 

 Humboldt recommended the erection of magnetic observatories all 

 over the world, and scientific men take observations four tirrfes in 

 a year in all parts of the world, and they find that the needle points 

 toward the west from China, and toward the east in California, 

 showing thereby that the magnetic line lies here in America. Dr. 



