BEIGHT CLOUDS ON A DARK NIGHT SKY. 17 



Now as that is the very effect which is experienced in the South every day 

 at Noon, as contrasted against Midnight, we might expect that our pheno- 

 menon was produced by an elevation of temperature in the air, without time 

 given to it to pick up moisture equivalent to its then increased Humidity 

 requirements. And this appears to have been the case to some extent, but 

 was certainly preceded at Aberdeen on the morning of the 8th, where the 

 influence began, by a very unusual decrease of the absolute amount of watery 

 vapour contained in the air, — however that decrease was operated. 



Hence in one way or another, dryness of the air was an eminent character- 

 istic of the atmosphere though for a limited period, near, or about, or shortly 

 preceding the time when the night clouds over Edinburgh appeared luminous 

 by excess of brilliancy in their reflection of the city's gas-lights. 



But what does that lead us to, as to the physical manner in which the 

 reflection was produced % 



Part III. 



Before entering on this last portion of the inquiry, let me further state, that 

 after many and many nights of clouds black on a gently translucent starry sky 

 subsequent to April 8, 1882; — there was another most remarkable example of 

 clouds bright on a black but still starry sky on Monday April 30, 1883. Those 

 unnatural looking bright midnight clouds, as they were wafted hither and 

 thither over the heavens by stray currents of air rather than regular winds, had 

 almost a fearful splendour, — reminding one of Salvator Rosa's dark Noon-day 

 pictures of white clouds overhanging deep rocky gorges among Calabrian 

 mountains black as midnight and teeming with treacherous banditti ; and I 

 much wondered that honest Edinburgh folk were not out on the streets in 

 crowds gazing at, and discussing the strange spectacle. So short-lived too ; 

 for the very next night was eminent for the normal blackness of its clouds 

 contrasted against the pellucid and star-bearing heavens between them. 



I wrote therefore to the Astronomer-Royal at Greenwich, inquiring whether 

 any of the more wide-spreading influences, causes or accompaniments of Aurora, 

 were manifested there, on the nights of April 8, 1882, and April 30, 1883, as 

 compared with the nights and days immediately before and after these two 

 dates. But the reply, as will be seen in Appendix 4, was entirely negative ; 

 for neither in Terrestrial Magnetism, Earth currents, atmospheric electricity, or 

 Sun-spots was there anything noteworthy going on at either of those times. 



Relieved therefore of any Cosmical phenomenon to attend to, — let us now 

 look at the matter in its more ordinary terrestrial character. 



On June 25, 1882, at the rather elevated station of Buxton, in high Derby- 



