80 
REPORT—1858. 
from a horizontal originating motion, so that the instrument gives in 
such cases an absolutely false indication. 
7(b). Mr. Budge’s inverted spring pendulum, restrained to a single semi- 
oscillation in one plane, offers some decisive advantages over ahy 
other form hitherto proposed of the pendulum seismometer. The 
whole length of the pendulum is elastic; and the rod being light, 
the whole weight by whose inertia it is bent may be considered as 
in the ball or bob. If © be the moment of resilience of the rod, and 
the deflection be not very great, the angle wpn=0, then— 
3(L tan g—2) =" ¥, 
L being the length, and d the horizontal ordinate of deflection of the 
pendulum. It is plain that although, like every other elastic rod, 
this will have a time of vibration of its own, and be therefore liable 
to part of the theoretic objections made to the simple pendulum on 
the same account, this form of pendulum will be “brought up” 
much more nearly within the true limits of the earth-wave amplitude 
in its horizontal component. 
Perhaps the ratchet and pall may not be the best mode, practically, 
of arresting its movement at the end of its first semioscillation, with 
sufficient delicacy, and other methods are obvious that may be ap- 
plicable; but if the elastic rod be a flat plate of sufficient breadth in 
relation to its thickness, and each rod or pendulum (of the four) be 
so placed, with reference to the cardinal points, that its broadest 
dimension shall be transverse to its normal plane of flexure, it is then 
obvious that practically we may neglect any flexion of the rod edge- 
ways, the four rods in section being posited thus (fig. 5)— 
N. 
Fig. 5. | 
peas 
| 
S. 
and that thus we obtain a flexure, for each pendulum, practically 
limited to its own vertical plane of oscillation, and so ean obtain, for 
any intermediate line of wave-transit between the cardinal points a 
good approximate resultant direction from the two adjacent com- 
ponent deflexions. Perhaps a flat ribbon-like rod of tempered steel, 
whose section should be a rectangle, with sides having the proportion 
of about 30:1, would be better than an elastic wooden lath; and in 
either case, it is probable that a tape or silk ribbon, fastened at the 
side 7, and passing with friction through asmall horizontal slot in the 
elastic rod, so as to be stretched by its deflexion and pulled through, 
would be the best and simplest mode of registering the deflexion, or 
the angle 0. 
While this appears to me the best of the solid-pendulum arrange- 
ments, I do not wish to be understood as recommending any one of 
the class. 
8 (0). Santi’s arrangement is of course subject to the objections made to all 
pendula. It possesses some advantage in separation of the results in _ 
