Mr. Mater on Earthquake Registration Instruments. 113 
alteration or re-adjustment is requisite at any time, beyond winding the clock, and 
changing the ruled paper. 
_ It has been suggested that a provision to guard against the effect of expansion 
in the mercurial columns, as affecting the points of contact, rs, &c., may be requi- 
site. The inventor is not of this opinion; but if it be so, the provision is easily 
made. Alterations of temperature will not affect the instrument in any other 
way, so as to derange its action. These instruments are intended for the regis- 
tration of those minute earthquake shocks which have of late been ascertained to 
be so frequent in almost all countries. The principle is applicable to those of 
greater magnitude and force ; but the instrument would require certain modifica- 
tions to meet the greater violence of the motions it would be then called upon to 
record. — 
VOL. XXI. Q 
