36 MODERN SEISMOLOGY 
would be about 240, or forty times that of the present Milne 
Seismograph. 
Although no seismograph at present gives an exact re- 
production of the earth movement in general, we ought not to 
regard the attainment of this as impracticable. The relation 
expressed by 
Yr2ey+My=-rNE 
is not the most general that may obtain between the impressed 
co-ordinate x and the recorded co-ordinate y. The general 
form is 
YPr2Zy+wmy= -rA (+ 264 47,74) 
and if it should prove possible to get a practical arrangement 
in which x=, and e=e, the latter being great, we should 
then come very near to a precise reproduction of uniform 
magnification. 
