178 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
Taking n,=50 and the rest of the data as before, we get r=1.32, and V(mazx) = 1000, 
the same value as before; but if we make x=1, the nearest practical value, we find 
V (maz) = 800, which is not very much less. By using steel ribbon for connectors at the 
axes, and between the pendulum and the levers, or by using one of the devices suggested 
by Dr. C. Mainka,' we could easily get rid of solid friction, and realize the theoretical 
values above. 
SUSPENSIONS OF HORIZONTAL PENDULUMS. 
There are 4 forms of suspension for horizontal pendulums: (1) The Gray suspension 
(figure 52); a horizontal beam carrying a weight presses against a point, and is sup- 
ported by a tie thru its center of gravity. Let F be the tension of the tie, P the pressure 
at the pivot, supposed horizontal, and W the weight; for equilibrium, these 3 forces 
must pass thru the same point and we must have 
F'cosa=W, or F'= W/cos a Fsina= P=Wtane (103) 
The friction at P depends upon the pressure there; and we see it is less as @ is smaller. 
This can be brought about either by putting the weight closer to the pivot or by length- 
ening the distance between the two points 
of support. By the first method we shorten 
the distance of the CG from the axis of 
rotation, and we change the values of the 
constants in the general equation; by the 
second method, these constants are not 
affected. 
(2) The Ewing suspension: this differs 
from the preceding only in replacing the 
pivot by a thin steel ribbon, thus doing 
away with the friction at this point. The 
horizontal beam is extended beyond the 
axis of rotation and is fastened to the axis 
by a steel ribbon. Professor Ewing sug- 
gested that a steel pin occupying the posi- 
tion of the axis of rotation, and connected 
firmly with the support, should pass 
through a slot in the beam, and thus pre- 
vent lateral movements of this part of the 
beam; but this pin introduces some fric- 
tion. This use of a steel ribbon has only 
lately been put into practice (by Professor 
Wiechert). 
‘ (3) The von Rebeur-Paschwitz suspen- 
sion (figure 53): the points of support are 
sharp steel points resting in agate cups, 
the upper one being turned to produce a 
supporting force. The three forces P, F, 
and W must meet in a point, which is ver- 
_ tically below or above the center of gravity. 

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1 Kurze Uebersicht tiber die modernen Erdbeben-Instrumente. Die Mechaniker, XV Jahrgang, 1907. 
Since the above was written Prof. C. F. Marvin has suggested a practically similar method for increasing 
the magnifying power, ‘‘A Universal Seismograph for Horizontal Motion.” Monthly Weather Rev., 
1907, vol. XX XV, pp. 522-534. 
