SOLAR HALO. 59 



produce a visible refraction through the ice crystals. 

 As the cloud strata containing the frozen moisture were com- 

 paratively very near the earth, any one or all possible condi- 

 tions mentioned might exist in the cloud formation in the 

 vicinity of Media. If the condition was a local one it would 

 in no manner affect a more perfect display at a point so far 

 away as Philadelphia, if the particular portion of the clouds 

 above the city contained all of the essential elements neces- 

 sary to form a complete figure. The last reason is the most 

 satisfactory and acceptable one, for if the ice field is admitted 

 to have been not more than four miles above the earth, the 

 thickening haze or the storm clouds which slowly (the maxi- 

 mum wind velocity on the 20th was 16 miles per hour) 

 approached from southwest, would certainly have obscured 

 the ice strata as viewed from Media at an earlier hour than at 

 Philadelphia, a distance of 14 miles eastward. The clouds 

 of the storm had doubtless commenced to concentrate in the 

 sky in the neighborhood of Media before the phenomenon 

 was first noticed, and had partly interfered with the display. 

 Of course, at points further east the halos might not have 

 been so obscured and may have appeared as perfect circles. 

 These reasons, taken into consideration with the different 

 effects that were possible where observations were taken from 

 different angles and elevations and from points considerable 

 distance apart, will establish a tenable and satisfactory expla- 

 nation for the apparent discrepancies in the minor details of 

 the phenomenon as observed at one place when compared with 

 those observed at another. 



Several observers reported that the sky inside the small 

 halo was unusually dark. This was, of course, an optical 

 illusion due to the effect of the radiance of the rings of glow- 

 ing light. If a careful study of the display had been made, 

 no difference in the shade of the sky inside or outside of the 

 halos could have been detected. 



Figure 2 shows the halos of May 20th as observed from the 

 Weather Bureau at Philadelphia, and it will be noted that the 



