Geophysical Institute-Alaska University— Wilson 189 



now being made by a low-brightness photometer developed by 

 Hulburt, and by a photoelectric recorder. The measurements 

 using Hulburt's photometer have been extended through the 

 first part of the 1949-50 winter season. Observations of the en- 

 tire sky were made at 15 ° intervals. They furnish an absolute 

 calibration of the zenith sky light recorder. Low values of 

 about 50 millimicrolamberts are found at the zenith. Horizon 

 values run three times as large. Typical night sky light contours 

 at College, Alaska have been reported in the following: 



Seaton, S. L., Night Sky Brightness at College, Alaska, J. Geophys. 



Res. 55,43-46 (1950) 

 Wilcox, J. B., A Survey of Night Sky Brightness at College, Alaska, 



Trans. Am. Geophys. Union, 31, 540-544 (1950). 



Values up to around 40,000 millimicrolamberts are observed 

 during auroral displays. 



Measurements of the intensity of the light from the zenith 

 night sky by the photoelectric recording system were begun in 

 September 1949. The recording system consists of an 1P21 

 electron multiplier type photocell feeding a two-circuit Brown 

 recorder. It gives a continuous record of the intensity on charts, 

 easy to reduce because of having a linear range from zero to 

 100,000 millimicrolamberts. This range has been found to 

 embrace all night sky light intensities from the darkest sky well 

 into twilight. These measurements are supported by the iono- 

 spheric and signal intensity contract of the Central Radio Prop- 

 agation Laboratory. Results have been reported in the research 

 reports to the National Bureau of Standards. 



Seismological Studies 



Alaska has several regions of earthquake and volcanic activity. 

 Two central regions lie along the Aleutian chain and in the 

 Tanana Valley. The recent work of Pierre St. Amand on the 

 earthquake swarm of late 1947 has been published in the paper 

 entitled "The Central Alaska Earthquake Swarm of October 

 1947" in the October 1948 issue of the Transactions of the 

 American Geophysical Union. 



