232 The Naturalist in Nicaragua 
We thus see that whirlwinds of great violence occur when 
the air is dry, and there can be no condensation. When, 
however, they are formed at sea, and occasionally on land, 
the air next the surface is saturated with moisture; and this 
moisture is condensed when it is carried to a great height, 
forming clouds, or falling in showers of rain and hail. This 
condensation of vapour is an effect, and not a cause, and 
takes place, not in the centre, but at the top or at the sides 
of the ascending column. ‘This is well shown in an account, 
by an eye-witness, of a whirlwind that did great damage near 
the shore of Lough Neagh, in Ireland, in August 1872.4 It 
was about thirty yards in diameter. It destroyed several 
haystacks, and carried the hay up into the air out of sight. 
It partially unroofed houses, and tore off the branches of 
trees. The railway station at Randalstown was much 
injured; great numbers of slates, and two and a half hundred- 
weight of lead were torn from the roof. When passing over 
a portion of the lake, it presented the appearance of a water- 
spout. On land everything that it lapped up was whirled 
round and round, and carried upwards in the centre, whilst 
dense clouds surrounded the outside and came down near to 
the earth. 
As above mentioned, I had in Australia many oppor- 
tunities of studying the dust whirlwinds; and as I looked 
upon them as the initial form of a cyclone, I paid much 
attention to them. Ona small plain, near to Maryborough, 
in the province of Victoria, they were of frequent occurrence 
in the hot season. This plain was about two miles across, 
and was nearly surrounded by trees. Incalm, sultry weather, 
during the heat of the day, there were often two at once in 
action in different parts of it. They were only a few yards 
in diameter, but reached to a height of over one hundred 
feet, and were often, in their higher part, bent out of their 
perpendicular by upper aérial currents. The dust and leaves 
they carried up rendered their upward spiral movement very 
conspicuous. No one who studied these whirlwinds could 
for a moment believe that they were caused by conflicting 
currents of air. They occurred most frequently when there 
was least wind; and this particular plain seemed to be 
peculiarly suitable for their formation, because it was nearly 
1 Nature, vol. vi. p. 541. 
