34 
REPORT OF MEETINGS. 
the insulating properties of the intervening air a spark passes 
between the two charged bodies. The lecturer then illustrated by 
experiments the production of spark and brush discharges, and 
showed some effective lantern slides of their counterpart in nature, 
forked lightning. The insulation of the air can be broken down by 
other methods of a silent nature ; by the use, for instance, of a 
flame, a radio-active substance, or a sharply-pointed metal rod. 
The last method is important in practical life, the lightning 
conductor being essential for the safety of large buildings. Although 
air may be generally regarded as an insulator, it is not a perfect 
one, and free charges are always present, produced at any rate to 
some extent, by the radium in the earth’s surface In fine weather 
it is found that there is always an excess of positive electricity in 
the air, and this travels as a current downwards to the surface of 
the earth. In wet weather the amount is much less, and may even 
be negative in kind. This prevalent stream of electricity probably 
has an influence on plant life, and the very striking results obtained 
by Lemstrong and by local agriculturists have chiefly been obtained 
by increasing the downward current. In explanation of the pheno- 
mena of atmospheric electricity, Mr. Tyndall mentioned the Wilson- 
Gerdien theory, which is that the water vapour in the air condenses 
on the negative charges and when falling as rain leaves behind the 
positive charges. It is doubtful whether this can be regarded as a 
complete explanation of the more violent effects of a thunderstorm. 
Finally, the lecturer contrasted the Aurora Borealis with the glow 
discharge in a vacuum tube, and mentioned the theory which 
attributes the appearance of the Aurora to the entrance of charged 
particles from the sun into the upper regions of the atmosphere, 
and their attraction by the magnetic poles of the earth. 
October 7th. — Sixth General Meeting. Dr. A. B. Browse ex- 
hibited the fruits of the flowering currant, the Siberian crab apple, 
and the American Blackberr}^ Mr. R. Priestley, one of the 
members of the Shackleton Antarctic Expedition, kindly sent for 
exhibition specimens of Antarctic lichens, including the one known 
as Tripe de Roche, which was used as an article of food by the 
explorers. Miss Ida M. Roper, F.L. S., read a short paper on the 
“ Nonesuch,” or “ Flower of Bristowe.” Mr. J. H. Priestley, 
B.Sc., F. L.S., University lecturer in botany, read a short paper on 
“Antarctic Rotifers and Low Temperatures.” Some material 
gathered on Mount Erebus was sent to the Bristol University, 
and the rotifers found in it were subjected, for periods of time 
varying from 24 to 72 hours, to a temperature of 108 degrees Faht. 
They were found to resist this temperature when in a dry state, but 
were killed by it when in a wet state. 
Mr. B. T. P. Barker, M.A., director of the National Fruit and 
Cider Institute, Long Ashton, said a few words about the “ Future 
of the Orchard,” and illustrated his remarks with a number of 
excellent lantern slides. He began by pointing out how the present 
conditions of orchards were unsatisfactory owing to neglect, pre- 
