TRANSACTIONS OF SECTION A. 471, 
The greatest rise of the barometer observed for twenty-four hours was ‘65 in. 
and the greatest fall -6. 
The fall of the leaves was zero on eighteen occasions, while it was as much as 
*5 mm. on four days. All the observations here given refer to a negative charge. 
2. On the Ionisation of the Atmosphere. By Professor A. ScuustEr, /.2.S. 
I have recently described! an instrument which allows us to obtain data for 
the measurement of the number of ions formed in unit time in atmospheric air. 
A number of observations have now been made which have led to an improve- 
ment in the apparatus and given some interesting results. The two data used for 
the determination are: 
(1) The number of ions, determined as in Ebert’s well-known apparatus; and 
(2) The measurement of the rate of recombination of ions. 
An improvement has been effected in Ebert’s apparatus by shortening the 
length of the tube and the rod, so as to reduce its capacity to about 6:4 electro- 
static units. This shortens the time in which an observation can be carried out 
from a quarter of an hour to about five minutes, The electroscope in the form 
now used by me is placed above the cylinder instead of below, which much lessens 
the deposit of dust on the insulating material and thus preserves it. 
The leak which always takes place when the apparatus is closed, and which is 
partly due to the leak of supports and partly to the continuous ionisation which 
takes place in confined air, was observed to be much increased whenever the 
apparatus was taken out of doors on a clear day. This effect was ultimately 
traced to convection currents in the apparatus, but the manner in which these 
currents act has not yet been ascertained. So far as my observations allow me 
to judge, they suggest the existence in the air of very slow-moving ions, which 
only give up their chatges when they are brought into contact with metallic 
conductors. 
The observations made on Exmoor, at a height of 1,400 feet, have led to the 
conclusion that the state of the air, as regards its power to allow ions to recombine, 
varies sometimes with great rapidity, especially near the time of sunset. The air 
on Exmoor was found to be very pure, so as to give a slow rate of recombination. 
On the other hand, the number of ions in general was rather less than that found 
near the level of the sea. Combining these results, I come to the conclusion that 
the number of ions found on Exmoor during the time the observations were made 
was considerably less than that commonly observed at lower levels. 
3. Discussion on the Radio-activity of Ordinary Matter. Opened by 
Professor J. J. THomson, /. 2.8. 
4, On the Radio-activity of the Hot Springs of Aiau-les-Bains. 
By Dr. G. A. Buanc. 
_A research concerning the radio-activity of both the thermal waters of Aix-les- 
ains was made by me recently. Their temperatures are respectively 47° and 
44° Centigrade. They both belong to the sulphur soda class. 
_ The fact which I principally wish to point out is the strong ionisation of the 
air inside the grotto where one of the springs is situated. Measures by means of 
an Elster and Geitel electroscope, surrounded by a wire netting, showed that its 
conductivity was about sixty times greater than that of the air outside; 1:75 lit. 
water of this same spring gave to 5 lit. air that had been repeatedly bubbled 
through it a conductivity rising to over 200 times the normal. The other spring’s 
\ Manchester Memoirs vol. xlvisi., No. 12 (£904). 
