906 Transactions of the American Institute. 



December 31st, 1868. 



Professor S. D. Tillman in the chair. Mr. C. E. Emery, Secretary. 

 IsOMETEICAL DkAWING. 



Mr. Joliii Johnson spoke of the utility of isometrical drawing, 

 Tliere is no part of machinery, he said, but can be represented by it. 

 All that is required is a T square and an equilateral triangle. Paral- 

 lel lines are drawn, and the T square, held in different positions, forms 

 the required angles-. The whole system of isometrical drawing 

 requires but the two instruments mentioned. 



Mr. Dudley Blanchard remarked that the onl}^ difference between 

 isometrical and the perspective drawing is that, in the former, every- 

 thing is supposed to be opposite the eye, each portion of the drawing, 

 while, in the latter, distant objects are of diminished size, which is 

 accomplished by means of lines converging to one point. 



Electric Induction, 

 Prof. Yanderweyde delivered a very interesting address on elec- 

 tric induction. Induction means that a body is induced to become 

 magnetic or electric from its own nature, without any magnetism or 

 electricity being communicated to it. In speaking of the induction 

 of galvanic currents, the lecturer said the induction only takes place 

 at the moment that the current commences. It then develops another 

 instantaneous in an opposite direction. "When the current stops? 

 another instantaneous current is induced in the same direction. On 

 this principle coils have been constructed, consisting of an inside wire, 

 which makes the current of the battery, and an outside wire, having 

 no connection with the battery, but in which the instantaneous cur- 

 rents are induced. These instantaneous currents may be, in large 

 machines, so strong that the spark of the charge has a length of ten 

 to sixty inclies. The professor here exliibited several small machines 

 of this kind, and next explained the action of the condenser connected 

 with those machines. They have a so-called contact-breaker, in order 

 to interrupt the current of the battery many times in a single second, 

 inducing as many secondary currents as this contact-breaker makes. 

 This contact-breaker will soon become destroyed by the electric spark, 

 therefore an arrangement has been invented to prevent this to a great 

 extent, which consists of an imitation of the Ley den jar on a very 

 extensive scale, however, condensed, in the space it occupies. This 



