122 KANSAS UNIVKRSITV QUARTERLY. 



wheel is fitted, not so closely, however, but that it may rotate and 

 slip from one end of the shaft to the other. To prevent any bind- 

 ing of the wheel upon the shaft, the wheel is made quite thick 

 through the centre, the length of the hub being equal to the radius 

 of the wheel. At one end of the shaft is attached a cross-bar, form- 

 ing a ^, each arm being equal to the radius of the wheel. The 

 extremity of one of the arms of the cross-bar is shaped into a knife- 

 edge, the extremity of the other arm being a point, which is fur- 

 nished with a shoulder to prevent its sinking beyond a certain point 

 in the material upon which it is worked. The knife-edge and point 

 both lie within the plane which passes through the centre of the 

 shaft. Passing through the cross-bar and shaft, and at right angles 

 to both, is attached a third arm. Through the extremit}' of this 

 third arm and parallel to the cross-bar is a set-screw, either end of 

 which may slide upon the surface operated upon. The object of 

 the set-screw is to keep the cross-bar always perpendicular to the 

 plane upon which it moves. The upper surface of the shaft is 

 graduated, either in the French or English system of units, as de- 

 sirable; if theEnglish system is used the graduation should read at 

 least as low as 1-64 of an inch. 



The instrument as it stands complete — the sharp rimmed wheel 

 \\pon the shaft, the three cross-arms, and the set-screw holding the 

 point and knife-edge perpendicular to the plane upon which it 

 stands, may be seen in the cut. 



i^ 



Cramp's Curvimoter, Fig. 1. 

 To operate the instrument we proceed as follows: — Take the 

 ©ross-bar firmly between the thumb and first two fingers, then place 



