106 



T. G. Mendenhall — Seismoscopes and 



an amount of friction which would be fatal. Ewing* has sug- 

 gested the use of some form of linkage in which only ties should 

 be used, so that flexible cords could be substituted for rigid bars. 

 No rigorously straight-line motion is susceptible of this con- 

 struction, but several close approximations may be utilized. 

 An approximation is all that is required, in a seismoscope, but 

 it must possess freedom of motion in all azimuths. Professor 

 Ames, of the Rose Polytechnic Institute, has devised a form 

 consisting of a combination of two linkages of the form invented 

 by Roberts. By arranging these in planes at right angles to 

 each other, freedom of motion in any azimuth is secured. A 

 heavy mass is pivoted at the tracing point and friction may be 

 reduced to a minimum by the use of flexible cords, fine wireSj 

 or by pivoting light rigid links. The suspension is approxi- 

 mately astatic, but sufficiently so for seismoscopic uses, and per- 

 haps for seismographs — It is shown in figure 3. 



A number of trials with several of these seismoscopes under 

 different varieties of disturbance show that all are not equally 

 sensitive to the same disturbance, however delicately they may 

 be adjusted. The mercury seismoscope is peculiarly sensitive 

 to disturbances produced by a slight jar of the table or support 

 upon which it rests. In this case the vibrations are generally 

 very rapid, probably from ten to fifty or more per second. It 

 may readily be adjusted to respond to extremely slight tremors 

 and besides it apparently affords the advantage of being set at 

 any time to a definite degree of sensitiveness. With the two 



* Memoirs of the Science Dept., Tokyo Daigaku, No. 9. 



