CONTINUOUS DAYLIGHT 325 



in the lower strata, the twilight is then correspondingly feeble. 

 But if, for any i^eason, there should be more of this reflecting 

 material present in the higher atmosphere than is ordinarily 

 the case, we should obviously have a stronger twilight than 

 usual. In fact, the brightness of the twilight would be 

 accentuated by such material in another way ; for by increas- 

 ing the density of the upper layers of the atmosphere it would 

 at the same time increase their refractive effect, and make 

 the sun's apparent depression beneath the horizon less than 

 normal. The result would be much the same as if we had 

 travelled some distance Northwards, and there seems little 

 doubt that the wonderfid ' glow ' of the past two nights is 

 to be attributed to such a cause. The remarkably long spell 

 of warm diy weather has produced abnormal conditions in 

 the different atmospheric layers, particularly in their tem- 

 peratures and in the amount of water-vapour and water-vesicles 

 present in them ; and to the unusual reflective and refractive 

 properties with which the atmosphere has thereby become 

 endowed we owe the brilliant midnight phenomena which 

 have been so greatly admired, as well as the curious effects 

 of miraye which have been observed in the neighbourhood. 



There has been absolutely nothing of an am'oral character 

 about the display, nor could the Zodiacal Light have had 

 anything to do with it, as that is too faint to be visible at 

 this time of the year." 



Note. — "To complete the scientific explanation of the wonder- 

 ful midnight ' glow ' observed on some recent nights, reference 

 may be made to the meteorological conditions prevailing over 

 our area at the time. The effect, as already explained, was 

 due to reflection and refraction. Anything abnormal in the 

 way of refraction of light waves through our terrestial atmos- 

 phere can occur only when the atmosphere is in a very 

 ^btidisturhed condition. Now for at least a week past that 

 has been so to a remarkable degree ; movement of the bai'ometer 

 over Scotland from day to day has been very slight, and 

 over an extended area there has been at any one time but 

 little vari^ition in atmospheric pressure," 



