SECTIONAL 'TRANSACTIONS.—A.1 357 
that the height of the ionised layer is very much increased during a magnetic storm 
does not seem acceptable. Hafstead and Tuve used 70-metre waves, which at vertical 
incidence would normally penetrate the lower region and be reflected by the upper 
region. An increase in the ionisation of the lower region would reduce the group 
velocity of the waves when passing up and down through that region, and thus give 
a fictitious increase in the height of the upper region, as measured by the echo-time 
method. In other words an increase in the ionisation in the lower regions produces 
an increase in the equivalent height of the upper region. Further evidence in favour 
of this alternative explanation is that during the storm which Hafstead and Tuve 
examined (October 18, 1928) the reflection of 70-metre waves was at times noted 
from the lower region, although reflection from that region was not observed on the 
days preceding and succeeding the magnetic storm. 
Mr. A. H. R. Gotptie. 
The electric field in magnetic storms has been deduced from computations of the 
position, direction and strengths of electric currents capable of producing the 
magnetic displacements recorded at Lerwick, Eskdalemuir and Abinger observatories 
during storms; and from comparisons of these records with those of other observa- 
tories, in particular Sitka, Sodankyla, Colaba and Mauritius. ‘The electric field 
so deduced appears in the northern hemisphere to have these features. Flowing 
northward across the latitude of about 30°N. and between the longitudes of 
about llh. and 18h., there is, as on quiet days, a great belt of positive electric current. 
This current, however, as compared with that of quiet days, is multiplied by a factor 
of the order of two to five according to the intensity of the storm. Of this magnified 
current the part lying between 18h. and about 14h. veers round as it proceeds north- 
ward until it passes along the auroral zone, appearing in the longitudes of 18h.to 
21h. as a greatly concentrated current flowing from about W.S.W.; the other part, 
namely that lying between about 14h. and 11h., bends in the other direction and 
- finally flows as a concentrated current from about E.N.E. along the auroral zone 
between the longitudes of about 7h. to lh. 
The heights of the current centres in the auroral zone lie mostly between 200 and 
350 km., but individual cases range from under 100 km. to over 500 km. Midwinter 
and quiet years are characterised by currents low in strength and in altitude and 
considerably inclined to the W.—E. direction. Other parts of the year and disturbed 
years generally are characterised by the opposite features. The stronger a current 
the greater appears to be the height of atmosphere to which it extends. 
Tn the auroral zone between the longitudes of 21h. and 24h. or Lh. is the meeting 
place of the westerly and easterly electric currents. What happens here evades 
ealculation, but at all events the amount of current that again emerges from the 
auroral zone and passes southward (to enter subtropical regions between the longitudes 
of about 19h. and Lh. as a northeasterly current) appears to be only about half of that 
which originally flowed northward. The region, therefore, in which visible aurora is 
most frequent is thus seen to be also the region of dissipation of positive electric current, 
that is, unless—following the Birkeland-Stormer theory—it be regarded as a region 
of origin of negative electric current, coming from the sun and injected at this point. 
For reasons given in the paper, the author is inclined to the view that the electric 
current, being mainly transverse to the magnetic field, is almost wholly a flow of 
positive ions, and that the electric field, both on quiet and on disturbed days, is 
generated on the sunlit side of the globe and mainly in tropical and subtropical regions ; 
and that the difference between quiet and disturbed days is one arising from the 
effect of the sun in controlling the conductivity of the higher atmosphere over the 
daytime region. The ionization of the atmosphere in auroral and polar regions is 
considered to arise mainly from the passage of electric currents generated in the 
sunlit regions of lower latitudes. 
Calculation suggests that forces of electrical origin may play a considerable part 
in modifying cr controlling the movement of the atmosphere at great heights, at least 
in the auroral zones. 
_ Dr. G. M. B. Dosson. F.R.8.—Recent Researches on Atmospheric Ozone. 
Proportions of the different gases in the atmosphere. Small amount of ozone. 
_ Reasons for special interest in knowing the amount of ozone. Connection with 
weather conditions. Distribution over the World and annual variations. 
