A. Milward, Esq., on the Motion of a Lava-Stream. 53 
In order to test the consistency of the lava, I threw seve- 
ral pieces of cold lava upon the surface of the stream, near 
the origin, where it was free from slag, and where, by the 
bye, it curved down slightly at the sides, being convex in form, 
These pieces were only a few pounds in weight, and if thrown 
with any force, it was very difficult to make them rest wheré 
they were cast; they bounded off just as if thrown upon 
a smooth sloping rock. By approaching as near the stream 
as the intense heat would allow me, I succeeded in causing 
some to remain on the surface, but generally close to the 
side. At length, however, I deposited a piece of a few 
pounds in weight just where the lava curved over from be- 
low, and in the middle of the narrow stream. After waiting 
until it had advanced curving upwards about a foot-and-a- 
half from the origin, I timed its rate of progress, and esti- 
mated that it passed over a foot in about twenty seconds. 
The heat was of course very great, as I stood within a yard 
of the red-hot stream, and the air for some distance around 
all these streams was in a state of constant agitation, just 
as it is seen over a heated stove, only to a much greater extent. 
At the distance of ten or a dozen yards from the origin, 
this stream, like all the others, and like those which had 
already grown comparatively cold, became covered over with 
scoriz, and gradually presented a broken surface of cinders. 
could have wished. Although I have a coloured drawing before me, in which I 
have endeavoured to give a general view of what I saw, yet, as it was not exe- 
cuted on the spot, but from memory, two days after, it cannot be anything more 
than a general resemblance. ‘The lines of scoriz were, as far as I can remem- 
ber, from yjth to jth inch wide, and separated by narrower intervals; they 
were a little broken and honeycombed. The great heat rendered it almost im- 
possible to approach sufficiently near to see how these lines moved past one 
another. I did not at the time remark any loops, or any tendency to conver- 
gence. The latter may have existed, but it must have been slight. The centre 
was less marked with scoriz, but they were not, I think, absent ; and the fainter 
indication I ascribed at the time to the greater heat. 
It has been suggested to me, that the differential motion is not sufficient to 
account for these appearances, and that they may be the result of some pecu- 
liarity in the manner of cooling. I would observe that if the differential motion 
caused only a tendency in the covering to crack ina slight degree, the con- 
tinuance of the motion and the radiation of heat through the crack, would gra- 
dually enlarge it. 
