TRANSACTIONS OF SECTION A. 469 
relatively slow decrease, as compared with the adiabatic rate, is due to the fre- 
quent inversions of temperature occurring at all heights in the free air. Whether 
the whole column of air in a cyclone is, on the average, warmer than that in the 
anticyclone depends chiefly upon whether its initial temperature at the ground 
is higher, as is usually the case when cyclonic conditions prevail in our latitudes. 
A more conclusive method of investigation is to plot the temperatures at the same 
heights in the free air during several consecutive days, when the barometric pres- 
sure and the air-temperature vary at the ground. This appears to have been done 
first by H. H. Clayton, meteorologist at Blue Hill, who utilised the daily kite- 
flights made there,’ one conclusion being that the maximum air-temperature at all 
heights (up to 12,000 feet) nearly coincides with, but slightly precedes the mini- 
mum of atmospheric pressure at sea-level, and that the minimum air-temperature 
at the different heights apparently occurs when the atmospheric pressure at sea- 
level is above normal, but usually some distance in advance of the maximum of 
atmospheric pressure there. Mr. Clayton now finds that the air in contact with 
mountain summits is colder than is the free air at the same height, which tends to 
invalidate the arguments against the convectional theory of cyclone-formation, 
based upon mountain observations. 
Kite-flights on Blue Hill are generally made once a month upon the days pre- 
scribed by the International Committee for Scientific Aeronautics. During 1908 
there were fifteen flights, the average of the highest points reached in each flight 
being 7,264 feet above sea-level, and the maximum height in any flight 13,970 feet. 
During the present year, from January to July inclusive, the nine flights have 
given an average height of 8,284 feet and a maximum of 14,660 feet. During 
the present summer, the writer hopes, by means of ballons sondes, liberated from 
St. Louis, to extend the observations of temperature in the free air to a height 
never before attained above the American continent. 
4. Problems of Astronomy. By Sir Daviw G11, K.C.B., FBS. 
5, Discussion on Units used in Meteorological Measurement. 
Opened by Dr. W. N. Suaw, F.2.8. 
6. On the Masses of the Stars. By Dr. H. N. Russewn. 
TUESDAY, AUGUST 23. 
The following Papers were read :— 
1. A Correlation between the Electric Conductivity of Air and the 
Variation of Barometric Pressure. By JOHN Don, ILA., B.Se. 
From their experiments already described in the ‘Annalen der Physik’ and 
elsewhere, Professors Elster and Geitel have shown that an insulated electrified 
conductor, in free air, undergoes a loss of charge which is to be attributed only in 
a small measure to imperfect insulation on the part of the supports. ' 
The rate of loss was found to vary according to the state of the weather, being 
increased by bright sunshine, by winds from hilly districts and by low atmospheric 
pressure, while it was diminished by fog and rain and cloud, and by the presence of 
dust and soot in the air. 
In a contribution to the ‘Archives de Science’ of Geneva, in January 1904 
1 See Blue Hill Observatory Bulletins, No. 1, 1899; and No. 1, 1900. 
