446 A. G. Compton—Method of obtaining Autographic 
record is a whole number of seconds in which an exact whole 
number of revolutions of the siren has been made; otherwise 
rangement is used. 
The fork N is mounted before the mouth of a Helmholtz 
resonator O, which is nearly or exactly in unison with It. To 
the small opening of the resonator se eted a cylindrical drum, 
of which the farther end is closed by a membrane to w ich 1s 
between the point and the disk being so adjusted that the at 
cuit B” is broken once at every beat, the beats noord: ier 
selves on the fillet as a row of dashes side by side with the 
other two records. 
