Miscellaneous Concluding Observations.
193
attached to the observation, and even in this case it is
impossible to decide from a single observation as to the
direction from which the disturbance comes, since the object
may be thrown either towards or away from the origin.
Bearing these preliminary statements in mind, we will now
proceed to discuss such observations as appear to be of use,
giving in the first place simply a list of the records:—
1. Colchester. Mr. J. B. Harvey's gaseliers apparently swung S.E.—N.W.
(p. 46).
2. Colchester. Mr. J. C. Shenstone's chimneys cracked at base round
N., E., and W. sides, and one of them displaced towards the S.
The movement here apparently had a N. and S. direction (p. 47).
3. Colchester. Lamps and chandeliers at Messrs. Joslin's observed to
swing N.N.E.—S.S.W, (approximately). Sides of iron bedsteads
resting against a N. wall fell over towards S. (p. 48).
4. Colchester. Chimney displaced towards E., and plates and other
articles fell towards the E. at Messrs. Hart and Fromant's.
House standing on slope from W. to E. Movement of house
apparently E. and W. (p. 50).
5. Colchester. The specimen card of shells in the Museum (p. 51) may
have been moved by an impulse from the S. The other objects
that were moved give no indication of direction.
6. Colchester. Wooden girder fell towards S. at Messrs. Davey, Pax-
man & Co.'s (p. 52).
determined from the dimensions of a body which has been overturned, is
a quantity not obtainable from an earthquake diagram. It represents
the effect of a sudden impulse. (4) In an earthquake a body is over-
turned or shattered by an acceleration, f, which quantity is calculable
for a body of definite dimensions. The quantity, f, as obtained from an
 
earthquake diagram lies between V / t and V2 / a, where V is the maximum
velocity, t is the quarter-period, and a is the amplitude. (5) The initial

velocity given in the formula V2 = 2a2 / b (for horizontal projection) used by
Mallet as identical with V2 in (3), are not identical quantities. (6) In

discussing the intensity of movement I have used the values V2 / a. (7) The
intensity of an earthquake at first decreases rapidly as the disturbance
radiates; subsequently it decreases more slowly. (8) A curve of inten-
sities deduced from observations at a sufficient number of stations would
furnish the means of approximately calculating an absolute value for the
intensity of an earthquake."—'Nature,' Oct. 1st, 1885, p. 527.