62 Chandler—An Improved Ilarmonograph. 
in which the sliding bars vibrate, the recording point being 
pressed upon this tablet by a spring sufficiently yielding to 
accommodate the distance varying with the obliquity of the 
recording rod. The two motions are made simultaneous by con¬ 
necting the parallel shafts bearing the driving cranks by means 
of gears. Obviously, by changing these gears, the periods of 
the two motions may be made to have any commensurable ratio 
desired. 
So, too, the length of each crank may be changed by a screw, 
and thus the amplitudes may be given any desired ratio. 
The shaft bearing the second crank, together with that crank 
and the attached sliding bar, the direction of the shaft remain¬ 
ing unchanged, can be revolved about an axis coincident 
in position with the central position of the recording rod, 
arid fixed in any desired place, thus determining the angle be¬ 
tween the directions of the two simple harmonic motions. 
The gear intermediate between those on the two driving shafts 
may be disconnected from them, and the phases of the two mo¬ 
tions may be adjusted at pleasure while they are independent of 
each other, thus securing any difference of epoch at the com¬ 
mencement of composition. 
Since the distances between the three planes containing the 
two original simple harmonic motions and the resultant are con¬ 
stant, the recording rod slipping freely through the intermediate 
joint, as the spring near the point lengthens the rod when it is 
oblique to the tablet, evidently the segments of the rod main¬ 
tain a constant ratio, and the resultant remains true. 
If the two simple harmonic motions have the same direction, 
is is evident that they will be traced along the same straight 
line and that their parts in the production of the resultant will 
be indistinguishable. But this difficulty can be removed in a 
manner similar to that of several other devices for the composi¬ 
tion of such motions, and with more than usual facility. The 
receiving tablet can be moved transversely with a uniform mo¬ 
tion by means of a rack and pinion, the pinion being borne upon 
the end of a shaft connected at pleasure by gears to the driving 
shaft of the first crank. 
Three or four simple harmonic motions may be compounded 
