140 
NATURE 
[JuNE 8, 1899 
to be correct, the observation of the meteor from Hertford 
would show that it was first seen when at a height of about 
thirty miles above East Harling, in the south of Norfolk, and 
that when above a point (indicated on the map by a star) about 
south-east of Ampthill, an explosion occurred which broke off 
part of the crust of the meteorite. At two other points (also 
marked by stars) in the neighbourhoods of Thame and of 
Abingdon and Wantage, explosions seemed to have occurred, 
the latter terminating the course of the meteorite. 
Some additional evidence is furnished by the grouping of the 
places where the sound of the explosion was accompanied by a 
distinct tremor. The two dotted curves on the map bound all 
places (with two exceptions) where the concussion was strong 
enough to rattle doors, windows, crockery, &c. The form and 
dimensions of the larger of these curves show that the first 
explosion must have occupied an appreciable fraction of a 
second. One or, perhaps, two curves might be drawn surround- 
ing the places from which tremors are recorded, but owing to 
the small number of such places between the dotted curves, it 
is uncertain whether it should be a single dumb-bell-shaped 
curve or two detached curves. It will be seen at a glance that 
the points which Mr. Fordham indicates for the Ampthill and 
Abingdon explosions lie very near the centres of the areas 
bounded by the dotted lines. The explosion above Thame was 
apparently too slight to produce any concussion on the surface 
of the ground. 
Tests.—(1) The extremely elongated form of the disturbed 
area, and its great length when the slightness of the vibration is 
great and widely-felt shock would now be attributed to such a 
cause, but there are certain local earth-shakes which may 
reasonably be accounted for in this manner. The fallof a heavy 
mass of rock is evidently capable of producing the observed 
effects such as are described below. For example, towards the 
close of last century, one or more of the great upright stones of 
Stonehenge suddenly fell. According to Mallet, ‘‘ the shock 
felt in all the neighbouring hamlets was so great that for some 
time, until the cause was discovered, it was thought to have 
been an earthquake, as in fact it was, though not produced by 
natural causes.” } 
Earth-Shakes in the Rhondda Valley.—In the Rhondda 
Valley in south-east Wales, there are frequent earth-shakes, 
which seem to be due to rock-falls in the deserted pit-workings 
by which the region is honeyecombed, In many of the pub- 
lished accounts of these disturbances, there is evidently much 
exaggeration; but there can be no doubt that the shocks are 
sometimes strong enough to cause windows and doors to rattle 
loudly, and even to give rise to a distinct rocking sensation, 
The shocks are accompanied by a noise which is generally 
compared to the thud produced by the fall of a heavy body, 
or to the report of a colliery explosion or a distant gun. 
They also seem to be felt quite as severely in the mines as 
on the surface, and alarm the men at work, who naturally 
attribute the phenomena to an explosion. On a_ recent 
occasion (October 16, 1896), a miner, who was working in 
the Gelli pit, informs me that he heard one loud boom, like 
the discharging of a shot in rock, followed by a slight rum- 
bling ; ‘‘ but others working in the same 
r = — 
Scale of Miles 
Brrminghars 
“Leamington 
* Sandford 
. Peon 
KC Mertpora 
Thaime * 
5 Bingdon 
Wantage 
. * Bisham — 
U Lamborne ope 
a 
= pit had a severe shaking, the tools spring- 
ing off the floor, the dust rising in clouds 
off the bottom.” Again, in the three 
oe cases (June 22, 1889; April 11, 1894 ; 
phe and October 16, 1896) which I have 
oo studied, the disturbed areas are roughly 
presieyitn Os, Filles circular, and the diameters are small, 
my Teese being, respectively, about one, six and 
three miles in length; and the second of 
these is said to have been by far the 
strongest recently felt in the district. The 
centres of the three areas are close to- 
gether, the two extreme ones being five 
miles apart, and they follow roughly the 
line of the Rhondda Valley. Now, the 
rapid diminution in intensity from the 
centre outwards implies a very shallow 
focus ; the shock and sound are by nature 
such as would be produced by the fall of 
a heavy mass of rock, underground pas- 
sages exist at no great depth, and sub- 
sidences at the surface are known to occur, 
ANS 
ae 
Mi Pes 
taken into account; the detached isoseismal lines in those cases 
where there are two or more explosions. (2) The sound is far 
more prominent than the vibration, which is never the case all 
over the disturbed area of an earthquake unless that area is a 
very small one ; also, the sound-area overlaps the disturbed 
area on all sides, and this is only the case with very weak earth- 
quakes. (3) The character of the sound, often consisting of a 
series of explosions. (4) The obvious transmission of the sound- 
vibrations through the air. Though I have examined many 
thousands of earthquake-records, the sound is almost uniformly 
described by the writers as of underground origin. (5) The 
vibration of doors, windows, &c., is evidently a concussion due 
to the impact of air-waves. Occasionally a tremor is actually 
felt, but, as in the case of a heavy thunder-clap, this is no doubt 
due to the same cause. (6) The evidence of barograms may be 
useful in those cases where there is reason to believe that the 
movement is not due simply to the disturbance of the recording 
arm. (7) The actual observation of the meteor, or, if the sky 
be covered, of the glare of its light through the clouds. 
Rock-FALLs IN UNDERGROUND CHANNELS. 
The fall of rock-masses in underground channels was for long 
regarded with favour as a possible cause of earthquakes.! No 
3 Ineed not do more than refer to the subsidences in certain well-known 
districts which are almost entirely undermined by coal-pits or brine chan- 
nels. The disturbance is sometimes described as resembling a severe 
earthquake, but there could hardly be more than a momentary confusion 
between the two phenomena. 
NO. 1545, VOL. 60] 
for houses have been destroyed in this 
way in many parts of the district. The 
evidence in favour of the view that the so-called earthquakes 
are spurious is therefore strong; but the crucial test, that of 
finding the fallen mass, has, so far as I know, never yet been 
satisfied. 
Earth-Shakes at Sunderland.—A similar, though less arti- 
ficial, origin may be urged with equal force for the remarkable 
series of earth-shakes which are occasionally felt in and near 
Sunderland. These have been described and the theory of their 
origin clearly worked out in an admirable paper” by Prof. G. A. 
Lebour, from which the following details are taken. The dis- 
turbances consist of sudden shakes, strong enough to make 
| crockery and windows rattle, often, but not always, accompanied 
by loud noises and dull rumbles. They are, moreover, singu- 
larly local, being almost entirely confined to the south-west 
part of the town, and, apparently, to certain linear bands 
within that part. As in the case of the Rhondda Valley shocks, 
the foci must be situated at slight depths, and the phenomena 
are such as would result from underground rock-falls. It is also 
certain that the necessary channels exist, for the magnesian 
limestone, on which Sunderland is built, is simply riddled with 
cavities of every size and shape, the origin of which is not far to 
seek. In the midst of the hardest and most compact portions of 
the limestone, there occur masses of soft pulverulent earthy 
1 Roy. Irish Acad. Trans., vol. xxi., 1848, p. 63. 
2 “*On the Breccia-Gashes of the Durham Coast and some Recent Earth 
Shakes at Sunderland.”” (North of England Inst. of Min. Eng. 7'7vaus. 
vol. xxxiii., 1884, pp. 165-174.) See also Geol. Mag., vol. ii., 1885, pp. 513- 
515- 
