﻿116 Prof. 0. Henrici on a 



for a really good instrument, and only wanted a practised 

 instrument-maker to realize it. I therefore called in 1892 

 on Coradi in Zurich, well known for his planimeters and inte- 

 grators. He set to work at once and sent me in a short time 

 a drawing of his construction, and it is due to his skill that 

 the instrument has, at last, reached a high degree of perfec- 

 tion. One Analyser has been made for the Guilds' Central 

 Technical College, which I shall describe. But I must 

 mention at once that Herr Coradi has since greatly im- 

 proved it, so much so that it is now one of the most perfect 

 integrators made. 



§ 6. Fig. 3 shows an instrument of Coradi's second design. 

 This will help to explain the first. 



There is first of all a solid frame whose base is a long 

 rectangle. It rests with three wheels on the drawing-board. 

 One of these, D, in the middle of the front, serves merely as 

 a support. The other two, E, E, are fixed to the ends of a 

 long axle which runs along the back of the frame. This may 

 be called the " shaft." It is placed parallel to the axis of x. 

 The instrument can, therefore, roll over the paper in the 

 direction of the ordinates y. 



If thus moved through a distance dy, the shaft will turn 

 through an angle proportional to dy. The shaft carries any 

 required number of short " cylinders/' In the figure there 

 is one marked C situated in the middle of the shaft. 



Above each of these cylinders is a vertical " spindle " S, 

 whose geometrical axis cuts that of the shaft. In the new 

 instrument each spindle carries one or two disks, H 3 , H 4 , in 

 fig. 3 ; but in the old construction one crown wheel with its 

 teeth pointing upwards, by aid of w T hich the spindle is turned. 

 At the lower end the integrating apparatus proper is 

 attached, which is quite different in the tw r o designs. But 

 before explaining this let me describe how the spindle is 

 turned. 



Along the front of the frame runs a carriage W, to which 

 the tracer F is fixed. This can be moved through a distance 

 equal to the base c to which the curve is drawn. To the 

 carriage a silver wire is also attached, which in the new 

 design is stretched along the front of the frame and then by 

 aid of guide-pulleys /, I over one of the disks H on top of the 

 spindle S (see fig. 3). By giving the disk H a suitable 

 diameter the spindle can be made to turn n times round, 

 whilst the tracer describes the whole base. In the old instru- 

 ment the wire only drives an extra spindle in the middle of 

 the frame, which by aid of wheelwork drives all the working 

 spindles. If the tracer on following the curve has reached a 



