IOWA ACADEMY OF SCIENCES. 183^ 



circles, but of 900 circles, in the short time of eighteen 

 hours. 



First of all, the pen was not made to move about a center 

 and describe a circle as in the ordinary process, but the 

 drawing-board was made to revolve and the pen held sta- 

 tionar3^ In its general outline the machine may be seen 

 in figure 20. AC is a long gas-pipe, selected on account of 

 its smooth surface and cylindrical form. At B the draw- 

 ing pen is attached. The operator governs it by means of 

 a long brass rod between A and B. This enables him tO' 

 lift the pen from the paper and lower it at will. Parallel 

 to this rod there runs a long capillary tube through which 

 ink is forced into the pen. The gas-pipe is fastened tO' 

 the bed of the dividing-engine DE. The drawing-board 

 is supported by a heavy steel shaft which rests in a conical 

 bearing at H. 



Figure 21 shows the method of attaching the pen to the 

 gas-pipe, A. Two brass bars, D B and B F, form a hinge. 

 The pen is fastened at B by an arrangement which permits- 

 its removal. Here may also be seen the glass capillary 

 tube through which the ink is forced into the pen. This 

 tube is fastened to the hinge in such a manner that the 

 pen can be filled at any position of the hinge. A rubber 

 tube, not shown in the drawing, connects this glass tube 

 with the capillary tube running to the operator's table. 

 At F there is a spring which tends to keep the pen pressed 

 mildly against the surface of the paper. When the oper- 

 ator desires to lower the pen he turns the eccentric at D' 

 so as to draw F against the pipe and the pen at B descends. 

 In order to lift the pen he reverses the process and the 

 spring, which is attached to a screw at D, is drawn in the 

 opposite direction. Thus one spring is made to do the 

 work of two. At one time there was a second spring 

 employed to raise the pen but it was found obnoxious and 

 was soon discarded. The screw which you see above the 

 pipe at A is not used when a drawing is made. Its pur- 

 pose is to hold the point of the pen in a constant position 

 so that depressions in the drawing table may be detected. 



