436 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



necting rod. Make the eccentric of three equi-distant rollers 

 and it would be possible. 



Mr. Babcock. — I think the angle at which the engine will start 

 depends entirely upon the size and condition of the bearing sur- 

 faces, and not upon the force which is applied to them. Let a 

 ■weight rest upon a level surface, and the greater the weight the 

 more power will be required to move it. This is just as it is at 

 the dead centre. Let the surface be inclined at a certain angle, 

 and the weight will just slide. That angle depends entirely upon 

 the condition of the surfaces. In other words, the angle of fric- 

 tion is constant with the same surfaces. When you get beyond 

 that angle the greater the weight the more rapidly it moves. In 

 the engine there is a certain angle of retardation, which depends 

 entirely upon the condition of the bearing surfaces, not upon the 

 size of the engine, or the length of the crank, or the diameter of 

 the cylinder. 



J^ew subject. — The subject selected for the next meeting was, 

 " The plating of metals," proposed by Mr. Stetson. , 



Adjourned. 



American Institute, Polytechnic Association, ) 



November 6, 186L J 

 Prof. Cyrus Mason in the chair. 



CRANK MOTION. 



Mr. Fisher. — Mr. Howell did not distinctly define the amount 

 of friction and leverage incident to the crank motion. Assuming 

 the friction of revolving bodies to be ten per cent., as a mean of 

 various estimates, if a wheel is so loaded that the centre of 

 gravity shall be at one-tenth the distance from the centre to the 

 circumference, a slight touch of the hammer would make it start. 

 Assuming the diameter of the shaft to be twe^ity inches, one- 

 tenth of the radius being one inch, adding half an inch for the 

 crank-pin, and a quarter of an inch for the joint at the cross- 

 head, 'we have a leverage of one and three-quarter inches, with 

 which a slight jar would start the engine, the pressure of the 

 steam being applied. This gives us three and a half inches dead 

 space within which power would retard the engine. But beyond 

 that there is a further space where the wear of the engine will 

 be greater than the useful result. There should, therefore, be 

 a leverage of two inches at least where the power would be lost. 



