398 TRANSACTIONS OF SECTION A, 
seven Westons similarly connected. The difference between the two sets 
was then measured on a Kelvin-Varley slide by the usual potentiometer 
method. 
The ratio obtained was 0°716953, which differs from the ratio 0°716958, 
determined by Wolff and Waters, by only seven parts in a million. This 
difference, small as it is, is entirely accounted for by the small differences, 
as ascertained by direct comparison between our cells and those made at the 
Bureau of Standards, 
8. On the Action of Alpha Rays upon Glass, 
By Professor E. Ruruerrorp, F,R.S, 
DEPARTMENT OF CospMicaL Puysics. 
The following Papers were read :— 
1. Results of some Recent Terrestrial Magnetic Work. 
By Dr. L. A. Bauer. 
The first slides shown related to the results obtained from the general 
magnetic survey of the United States, chiefly executed under the author’s 
direction during the period 1899-1906. On the average, the three magnetic 
elements have been determined, with every possible care, at one station 
for every 973 square miles; hence the average distance apart between 
stations is thirty-one miles. The iso-magnetic lines reveal great irregu- 
larities, and it has become evident, from a preliminary analysis, that it 
would not be possible to establish a general formula for the earth which 
could even approximately represent the actual magnetic conditions observed, 
unless a prohibitively large number of terms were embraced in the series. 
This survey afforded opportunity for a test as to how closely the observed 
magnetic forces could be referred to a potential, or, in other words, as to 
the existence of possible vertical electric currents passing from the air into 
the earth, or vice versa, The line integrals were calculated around various 
closed circuits, one embracing the whole of the United States. The 
cbservational quantities could be represented by a potential to within about 
3h part, whereas the observational error was about ;4, part. Hence there 
was, apparently, a small outstanding portion that might have to be referred 
to non-potential forces, such as vertical electric currents. 
The question as to the existence of such currents can further be tested 
by the recent magnetic work in the Pacific Ocean of the Carnegie Insti- 
tution of Washington, and the calculations are now in progress. Further- 
more, by the end of 1910, in view of the work already accomplished and 
the results to be obtained from the ocean magnetic survey just begun in 
the Atlantic, it will be possible to make one or two complete circuits of 
the earth on the basis of freshly acquired data. Views of the vessel 
Carnegie, engaged in the ocean work, were shown, and the methods of 
observation briefly stated. 
Next, brief consideration was paid to various kinds of magnetic dis- 
turbances, e.g., the magnetic one associated with the Mont Pélée eruptions 
of May 8, 1902, and occurring simultaneously over the whole earth, and 
next the evidently purely mechanical one at the time of the San Francisco 
earthquake, April 18, 1906. The latter effect was propagated with the 
speed of the long seismic waves, and was recorded at the Coast and Geodetic. 
magnetic observatories at Honolulu, Sitka, Baldwin (Kansas), and 
Cheltenham (Maryland). The time of beginning agreed very closely with 
that given by the seismographs. 
In conclusion, a brief résumé was given of an investigation on the 
relation between solar activity and terrestrial magnetic activity conducted 
