ISOSEISMALS: DISTRIBUTION OF APPARENT INTENSITY. 327 
below was designed and was later constructed by the Mechanical Engineering Depart- 
ment of Stanford University. 
In designing a shaking apparatus to imitate an earthquake, certain conflicting con- 
ditions must be taken into consideration. It would seem that the apparatus ought to 
be on as large a scale as possible, but if it is on a large scale, it must needs be very expen- 
sive. If the linear dimensions are increased in any ratio, say trebled, the volume, 
weight, strength, and power to operate must be increased in the cube of this ratio; hence 
if the linear dimensions are trebled, these quantities must be increased 27-fold. ) More- 
over, it is obviously impossible, at any cost, even to approach the scale on which nature 
acts. With these considerations in view it was decided that the scale of the apparatus 
should be as small as is consistent with obtaining results from which general conclusions 
might be drawn. 
Earthquake motions are exceedingly complex, but it was not thought worth while 
to imitate this complexity, but rather to corfine the shaking motion to a simple to-and- 
fro horizontal motion in one direction. 








Fic. 60. — Diagram of construction of apparatus used in experiments; 
A side elevation of the apparatus as finally constructed is shown in fig. 60. A is a 
direct current motor, B is a balance wheel weighing about 75 kg. The connecting rod, 
instead of being driven by an eccentric, is driven by an adjustable crank, H, which 
allows the stroke to be adjusted to any value up to 10 cm. Cis the car, whose internal 
dimensions are 100 x 86 x 30cm. The car is carried on steel rollers, D, D, 4 em. in 
diameter. The car, balance wheel, and motor were all mounted on a heavy framework 
securely bolted together. The drum G was mounted on an entirely independent sup- 
port. A paper wrapt around the drum received traces representing, (1) the motion of 
the car, (2) the motion of a block 1’ set in the material on the ear, and (3) the beats 
of an electromagnet J, electrically connected to a seconds pendulum. (The pencil 
actuated by the electromagnet was on the same side of the drum as the other tracing 
pencils, instead of being on the opposite side, as shown in the figure.) The block F was 
30 em. square and was furnished with side pieces running 6 cm. down into the sand, so 
that its motion was necessarily the same as the material immediately under and sur- 
rounding it. 
The experiment consisted in loading the car and then shaking it by means of the motor, 
with various amplitudes and frequencies. While the car was being shaken, the drum 
was rotated by hand, and the relative motion of the car and the block embedded in the 
load was determined by measuring the traces on the paper wrapt around the drum. 
The material with which the car was loaded was limited almost exclusively to ordi- 
s 
