178 Trans. Acad. Sci. of St. Louu. 



enclosing these suspension fibers, was a lateral brace 

 formed of two bars of hard rubber, about 30 cm. in 

 length. The ends of these bars formed a right angle 

 against which the vertical suspension cylinder was 

 pulled. These rubber bars formed the ends of two long 

 bars of wood attached to the tops of instrument cases 

 along adjoining sides of the room. The bars were also 

 supported by a framed structure. Silk cords attached 

 to the cases ran along the two bars and were tied to the 

 suspension cylinder. Weights distributed along these 

 cords served to hold the cylinder against the ends of the 

 rubber bars. Vibrations of the suspension cylinder were 

 thus wholly eliminated. The torsion head forming the 

 top of the cylinder was provided with a rod which ex- 

 tended radially outward to a distance of about 20 cm. 

 By this means the torsion head could be turned in order 

 to put the suspended masses into vibration. The top of 

 the suspension cylinder had a similar rod clamped to it 

 having an upward projecting stop, by means of which 

 the torsion head could be returned to the original posi- 

 tion. Change in the temperature of the air within the 

 shield resulting in a change in volume was provided for 

 by the outflow or inflow around the torsion head. 



The enclosing case was of the general form used by 

 Cavendish. In the early part of the year it was formed 

 wholly of metal. It rested upon insulating blocks of 

 rubber, which were mounted upon two long pieces of tim-. 

 ber having a cross section of 4x4 inches. These timbers 

 rested upon a massive table, which was on a floor of re- 

 inforced concrete within a building having granite walls. 

 At the central part of the metal shield the dimensions 

 were 5x5 inches. A narrow slit on one side covered by 

 a small plate of glass sealed to the shield, served for ob- 

 serving the movement of the suspended masses by means 

 of a telescope and scale. At the outer ends of the shield, 

 the lateral dimension was about 15 inches. This form 

 was chosen in order that the suspended masses and the 

 brass tube upon which they were mounted could be in- 



