273 



the locomotive by subjecting them to saturated steam of about the same 

 temperature as that recorded in the experiment. The reading of one was 

 accepted as standard, and the errors of the other two determined. 



An experimental stx'dy of the action ok the coiNTKRiiAi.ANi k in LOCO.MO 

 TivE dkivewjieels. By Wm. F. M. Goss. 



In the mechanism of the locomotive, the mass of the reciprocating parts 

 (piston, piston rods, crosshead, etc.) is balanced to a greater or less extent, 

 by the addition of masses to the drivers, known as counterbalances. But 

 the counterbalances move in circular paths, so that it is only the horizon- 

 tal component of the radical force derived from them that serves to neu- 

 tralize the effect of the reciprocating parts ; while the vertical component 

 of these counterbalances is an unbalanced force causing the pressure of 

 the drivers on the rails to vary with every revolution. The extent of the 

 disturbing eft'ects of this unbalanced vertical component has long been 

 a question of serious concern to the locomotive designer; but in this 

 country, at least, they have found but little light to guide them. It has 

 been difficult to ascertain enough of the conditions existing at any phase 

 of the wheel's motion to serve as a basis for satisfactory mathematical 

 work, and no solution has as yet been presented which will enable the 

 designers to anticipate effects which are incident to the action of the com- 

 pleted machine. Practical demonstrations, however, are not wanting. 

 Bridges are shaken until they fall, and rails are actually crooked under 

 the stresses brought upon them by locomotives passing at high speed. 



It occurred to the writer that in the case of the Purdue experimental 

 locomotive a study could be made of the extent of this changing pressure 

 of the wheel upon the rail, by feeding a wire under the wheel and by 

 making use of the resulting variations in its thickness. This was first 

 accomplished last spring, but the most satisfactory results have been ob- 

 tained during the term just closed. A light mark made with a cold chisel 

 across the face of the wheel leaves its impression in the wire and furnishes 

 the desired reference point, by means of which particular effects may be 

 connected with their appropriate wheel positions. 



The following, concerning one of the rear drivers, may be of interest: 



The pressure which this wheel exerts upon the rail when at rest is 7 

 tons, and its counterbalance, reduced to the radius of the crank pin, weighs 

 18 



