Vol. 6, 1920 
GEOPHYSICS: L. A. BAUER 
575 
3. Efect of Altitude upon the Earth's Magnetic and Electric Elements: 
One of the important problems, both from a practical and a theoretical 
standpoint, is that of making magnetic and electric observations in the 
upper regions of the atmosphere. A number of investigations of extreme 
interest fall under this head. How the magnetic data for the United States 
may contribute towards the solution of some of the problems has already 
been stated. The preliminary analysis mentioned gave some indication 
of dependence of vertical-intensity residuals upon altitude. A joint in- 
vestigation by the Department of Terrestrial Magnetism and the United 
vStates Coast and Geodetic Survey was made of the mountainous region 
about Pike's Peak, Colorado, directly after the eclipse observations of 
June 8, 1918. The magnetic stations ranged in altitude from about 6,000 
feet to 14,000 feet. Whether any definite result may be derived from 
such mountain observations as to rate of variation of magnetic elements 
with altitude, in view of the minuteness of the probable variations, de- 
pends upon the successful elimination of the local disturbances caused by 
magnetic rocks. It was found that the region investigated was not 
wholly free from such disturbances. It will be necessary for the solution 
of the problem to devise instruments of sufficient sensitiveness and sta- 
bility to make possible magnetic observations of the required accuracy 
in air ships. To show the necessity of altitude magnetic observations, it 
will suffice to say that an infinite number of distributions of magnetic and 
electric systems within the earth may be found which will satisfy observa- 
tions made simply on the surface of the earth. 
Complete atmospheric-electric and radioactive observations in the 
upper regions of the atmosphere are of fundamental importance to the 
problems of the earth's electric field: of its maintenance, and of its varia- 
tions. It is very much to be hoped that such observations may soon be 
systematically carried out in the United States. 
4. Variations in the Earth's Magnetic and Electric Phenomena: The 
study of these variations opens up a wide field of research of interest not 
only to the Section of Terrestrial Magnetism and Electricity but also to 
other sections of the American Geophysical Union. In investigations as 
to a correspondence between manifestations of the earth's magnetic, 
or electric, activity with the Sun's activity, one of the fundamental ques- 
tions is what to take as the complete measure of activity, either for the 
earth or for the sun. This question also enters into certain meteorological 
investigations. In this way, and as appears later, some of the problems of 
Section d (Terrestrial Magnetism and Electricity) also touch upon some 
of those of Section c (Meteorology). The following quotations from the 
Annual Report of the University of Cambridge for 1919, relating to in- 
vestigations made by Dr. C. T. R. Wilson at the Solar Physics Observ- 
atory, are of particular interest here : 
