34 REPORT—1850. 
Lastly, the observer of the New Zealand earthquake of 1848 records, that 
certain vessels of milk had a movement of rotation given to the fluid they 
contained, so as to accumulate the cream in the centre. (Westminster Re- 
view, July 1849, p. 402.) He appears only to énfer rotation from the accu- 
mulation of the cream in the centre. This accumulation might take place 
from oscillation in one plane only in a shallow milk vessel; but admitting 
at once the rotation, there is no ground for concluding vorticose motion in 
the shock from this. Indeed this observer himself goes much nearer it when 
he says, “‘ Some of the shocks had a cross motion,” &c. It is not easy to say 
what this exactly means ; but one can readily see, that if oscillation be given to 
a fluid in a circular vessel, first in one plane, and then, while this continues, in 
another plane forming an angle with the previous one, by a subsequent shock 
whose direction was different, rotation will be at once communicated to the 
fluid ; and this I believe to have been the solution of this case. 
M. Place records, and the same has been done by others, that in some of 
the South American earthquakes a conical cavity was found worked out in 
the ground, around the base of the trunks of palms and large trees. This 
would appear at first sight like a vorticose twisting round and round of the 
stem, so as to work out this hollow; and such a twisting actually took place 
no doubt; but any inverted pendulum with an elastic stem, such as a tree is, 
the centre of gravity of whose head does not coincide with 
the vertical plane passing through the centre of elastic effort 
of the stem, will thus rotate from a single impulse given in 
one right line; and it is the tendency to do this that con- 
stitutes the vice of all inverted pendulums as seismometers. 
While, however, I consider it proved that there is no 
evidence whatever for any other mode of propagation or 
translation of the earth-wave or shock than that of a right 
y—— line in any given direction towards the earth’s surface, 
} or parallel to it, 1 am prepared to admit that upon 
iy |) 
͵ Uj this very principle it is possible for a most violent 
ΗΠ Ἴ wrenching or twisting motion to be given to any spot 
ἡ ζ of tolerably large size upon the surface of the earth. 
Ἰ Uj If, for example, from a centre of impulse at a great 
depth below the centre of a surface comprehended by 
a circle of, say a mile in radius, and in a direction to meet the extremity of 
any given radius, a shock be transmitted, and that by rapid and continuous 
change in the nature and direction of the impulse, a quick succession of 
such shocks be transferred round the whole circumference of this circle, 50 
as to describe by their path a cone in the solid earth, whose apex is the centre of 
impulse, and whose base is the circle on the surface before defined, then as 
each portion of this circle is lifted in rapid succession, it is manifest that all 
upon and within it, and by connection of parts all for a distance, gradually 
disappearing around it, will be shaken by a violent wrenching motion, which 
will make every body upon the surface describe an irregular conical figure 
in space also. 
But while it is thus worth while to show that such a complex movement 
may result from simple rectilinear wave motion, I have been able to find no 
record that gives the least presumption of any such phenomena having ac- 
tually occurred, when the facts are rightly interpreted in accordance with 
admitted mechanical laws. 
Let it be noticed however here, that there are, ἃ priori, strict grounds of 
exact science for believing, that in all great shocks of earthquake, besides the 
transmission of the great wave in the normal direction from the point of 
origiual impulse, there will necessarily be transmitted one, if not two sets of 
