Nipher—Gravitation and Electrical Action. 169 
a modified form of that used by Cavendish. The sus- 
pended masses consisted of two lead tubes, each being 
about 15 em. in length, each having a mass of 50 grams. 
They were mounted around the ends of a brass tube 91 
em. in length, and having a mass of 30 grams. This tube 
was suspended upon two loosely twisted threads of silk 
fibers, 180 cm. in length, whose distance apart was ap- 
proximately 0.4 cm. The twist was removed from these 
threads by hanging upon each a mass of 65 grams. This 
formed a very sensitive bifilar suspension. The sus- 
pended masses were wholly surrounded by a metal shield 
of rectangular form 10x12.5 em. in eross section. The 
suspension fibers were enclosed in a metal tube, having 
a torsion head at the top, thus providing means for prop- 
erly adjusting the position of the brass tube. The ends 
of the rectangular shield were provided with metal caps, 
fitting closely into its ends. They entered the shield a 
distance of 2.5 em. An opening at the middle of the 
shield, in front of a mirror mounted upon the suspen- 
sion wire, served for observation of position by means 
of a telescope and scale. This opening was covered by 
a sheet of glass which was sealed to the shield by means 
of Sealing-wax. The window was covered with a metal 
wire screen having about 5 wires per running em. The 
mirror was observed through this wire screen, the tele- 
Scope being focused upon the scale at the telescope. A 
change of one scale division represented a change of 2.36 
minutes of are in the position of the suspended tube. The 
Suspended masses and the brass tube on which they were 
mounted were surrounded by sheets of asbestos paper, 
which fitted into the caps at the ends of the shield, and 
fitted loosely the interior of the shield. These two lin- 
ings formed extensions of the end caps and were in- 
tended to prevent a convection of the air within the shield. 
The large masses each consisted of two fifty-pound 
Weights placed one upon the other and mounted upon 
“avy columns of rubber. They were separated from the 
metal shield by a space of about 2. em. In this space was 
