272 KIMBALL: ATMOSPHERIC HAZINESS DURING 1912 



Astronomical observations. While most of the repHes to the 

 circular letter addressed to members of the Astronomical and As- 

 trophysica Society of America were to the effect that no data 

 had been obtained bearing upon the question of a diminution in 

 atmospheric transparency during the latter part of 1912, a consid- 

 erable number furnished data that were confirmatory of such a 

 diminution. For convenience of discussion these data were 

 divided into four classes, as follows: 



a. Visual observations of a general whiteness of the sky and a 

 lack of transparency of the atmosphere. 



b. Instrumental determinations of atmospheric transparency, 

 which generally showed a decrease commencing with June or July. 



c. Unsatisfactory results in astronomical photography, and a 

 general increase in the exposure time required. 



d. An observed increase in the brilliancy and duration of twi- 

 light colors. 



These last were confirmatory of observations made by Weather 

 Bureau observers, which indicated that twilight colors were unusu- 

 ally brilliant in October and November, altho at a few stations the 

 colors were the subject of remark as early as June. 



The decrease in atmospheric transparency as determined by 

 observations classified under b and c was generally estimated at 

 from 10 to 20 per cent. 



A few observers detected a change in the color of sunlight 

 as well as in that of sky light, apparently due to the excessive 

 absorption or scattering of the shorter wave lengths. 



Pyrheliometric observations. At Mount Weather, during the 

 last half of 1912, the solar radiation intensities measured with the 

 sun at zenith distance 60° averaged only 83 per cent of the corre- 

 sponding intensities measured under normal conditions. At 

 Madison, Wisconsin, they were 86 per cent of the average; while 

 at Lincoln, Nebraska, in November, 1912, they averaged only 82 

 per cent of the intensities measured in November, 1911. 



Sky light polarization. At the point of maximum polarization 

 the percentage of polarized light averaged about 20 per cent less 

 during the last half of 1912 than the average under normal con- 

 ditions. Also, the solar and anti-solar distances of the neutral 



