SMALL WHIRLWINDS. 99 
sometimes cause them to collapse and be dispersed, while at 
other times whirls may be seen passing through trees, bushes, 
fences, and even coming in contact with houses without being in 
any way affected. By observing these effects I was assisted in 
arriving at the cause of these whirls as mentioned in section two, 
viz., whether caused by ascending or opposing currents. ‘Those 
eddies caused by opposing currents of air are easily dispersed 
either by standing in them or by coming in contact with bushes 
etc., but a whirl produced by an ascending current is more violent 
in its rotatory motion, and on meeting with any temporary 
obstruction, and being broken, this violent up-current is very 
likely to restore the form of the whirl by reuniting with its upper 
part. 
Hence those whirls produced by ascending currents are not, as 
a rule, much affected by coming in contact with obstructions, for 
as soon as the axis of rotation has passed the object, the up-current 
is restored as suggested. As an example of each I may mention 
that I saw one large whirl pass through a two rail fence, but on 
coming in contact with a paling fence about ten yards further on 
it completely collapsed. On the other hand I saw one, apparently: 
no larger or different to the general species, come in contact with 
the Walbundrie Hotel (February 1892), and instead of being 
dispersed, it carried away two of the verandah posts and sent the 
sheets of iron flying. I have only seen one instance of whirls 
coming in contact with one another, viz., that mentioned on my list 
for March 15, 1893. In that instance, five small whirls (left 
handed), were chasing each other round in acircle about seven feet 
in diameter. They eventually conjoined, and proceeded as one 
_ whirl, still revolving in a left handed direction (as in Fig. 2). I 
watched it travel about fifty yards through the bush, when I lost 
sight of it. 
Sometimes these whirls are seen under circumstances that make 
them very striking. For example, on Saturday March 19, 1892, 
(no barometrical record) wind south—I was walking through a 
stubble paddock that had been burnt off during the day, but was 
