340 



ILLINOIS STATE ACADEMY OF SCIENCE 



EFFECT OF LUNAE GRAVITY UPON A QUARTZ 

 THREAD BALANCE 



R. C. Haetsough^ Illinois Wesleyan Univeesity 



The construction and description of the apparatus. 

 The construction of the balance is somewhat after Threl- 

 f all's "Gravity Balance." The chief addition is a long 

 vertical lever arm and suspended mirror for magnifying 

 small movements. This is due to Lord Kelvin in his 

 ^' Lunar Disturbance of Gravity" experiments. 



The shape of the apparatus is of a large T ; the horizon- 

 tal part is 60 cm. long and the vertical part is 50 cm. long. 



Quartz Rod 



Wt. I^ever, 

 (Quartz) 



tT 



Quartz Thread 



^Observing Lever (Quartz) 



<Sllk Fiber 



6 



^^mall mirror 



Instead of silvering, plating and soldering the mounting 

 of the quartz thread, type metal was found entirely satis- 

 factory and much surer and quicker of application. 



These specifications, together with the following draw- 

 ing of the apparatus, will give a correct idea of the bal- 

 ance as used. 



Size of quartz thread 0.04 mm. diameter 



Length of quartz thread 55.7 cm. 



Length of short weight-lever 2.0 cm. 



Length of long observing-lever. . .26.5 cm. 

 Weight on weight-lever 0.10 gm. 



