A WHIRLWIND AND WIND-RUSH AT GOSI'IELD. 
9 
quantity of brown dust. This seems strange in view of the 
fact that the ground traversed was mostly pasture and very 
wet, owing to the thunder-storms earlier in the day. Some 
of this dust Was gathered, perhaps, from the ground below 
the trees, which were uprooted. This can hardly have been 
the case, however, with the dust which the Messrs. Ardley 
saw carried up actually at the place of origin of the storm and 
immediately after it began. The extensive transport of dust 
and dirt was observed also (as will be remembered) in the case 
of the Writtle storm. 
It is curious that two of these very-striking phenomena should 
have occurred, no more than sixteen miles apart, within a period 
of no more than twenty-one months ; also that both should 
have followed a more-or-less north-easterly course. 
DISCUSSION. 
Mr. F. J. W. Whipple read the following comments, written by Sir 
Napier Shaw, F.R.S., Chairman of the Meteorological Committee :— 
" So far as I can make out, this whirl arises from some local instability 
in the upper air, which gives rise to a local rotation sufficiently rapid to 
balance a distribution of pressure with a low pressure core. This dis¬ 
tribution of pressure is then transmitted to the surface and the air is 
gradually sucked out of the core and rotation set up. When the core 
reaches the surface, it is very bad for the surface, because the core is 
protected by spin, except just at the surface, and there the low pressure 
at the centre has to be supplied by air which passes along the surface 
and gets up spin as it goes. In so far as the core is fed at all, it is by what 
moves along the surface, which cannot get up enough spin to make a 
balance. So the arrangement becomes very like a vacuum cleaner on a 
large scale, with a “ hose ” made of air spinning so fast that it can resist 
the external pressure. Passing over water, the air going to the centre 
blows the water into spray, which is carried to the low pressure in the 
middle.” 
“ The mechanical process at the bottom is thus sufficiently evident, 
but the mechanism of the top is still unknown. There is something there 
which keeps up a suction and so maintains a low pressure along the core 
of the hose. The effect can be imitated by a fan-wheel in a solid lid or 
by a gas-jet in a tube leading from a solid lid ; but nobody has yet shown 
how to set up a whirl of this kind when there is no lid. One can describe 
possible conditions that would meet the case, but cannot realise them 
experimentally, because one cannot work on a sufficiently-large vertical 
scale.” 
Mr. Whipple also showed lantern-slides illustrating the damage done 
to buildings by a tornado in America. He invited members who were 
so fortunate as to have the opportunity to observe such phenomena to com¬ 
municate at once with the Meteorological Office. Great interest attached 
to the movements of the clouds during the passage of the tornado. It 
