GRAVITATIONAL METHODS 



299 



tective tubes containing the lower weights are unscrewed and packed 

 separately for transport, as are also the weights and the brass suspension 

 wires. The torsion wires and the balance beams remain in the instrument 

 during transport; the balance beams can be locked by turning the milled 

 knobs on the short side of the casing. 



Intercepting mirror 

 Lamp 



Fixed mirror 

 Adjustable mirror 



Compass 



Balance beam 



Contact clockwork 



Lower -weight — 



Plate-holder attachment 

 Torsion head 



Platinum wire 



Level 



Balance beam mirror 



Arresting mechanism 



Upper weight 



Driving clockwork 

 Ring gear 



— Protective tube 



Fig. 160. — Large torsion balance (in section). (Courtesy of American Askania 

 Corporation.) 



A compass is mounted on the lid of the outer casing and is used for 

 setting the upper part and the stops in the central portion of the instru- 

 ment in the meridian. The upper part of the instrument can be set into 

 an exactly vertical position by means of two tubular levels. The torsion 

 heads permit micrometric twisting, raising, lowering and lateral shifting of 

 the torsion wires and hence of the balance beams. 



