1874.] Composition of two Harmonic Curves. 397 



vibrations in a given time of the pencil and paper, and which will be the 

 curve of pressure for the interval corresponding to this ratio. 



The manner in which these three motions are combined in the machine 

 is as follows : Two vertical spindles, A and B, revolving in a horizontal 



plate carry at their lower ends each a crank, C and D, and at their upper 

 ends each a wheel cut with a certain number of teeth ; these two wheels 

 can be connected by means of an intermediate one, as is seen in the figure ; 

 and since either wheel of the pair can be replaced by another with a different 



