appears to subsist between it and the Formation of Clouds. 27 



rose, when the rain ceased and the clouds resumed the cirro- 

 stratus character. This interesting phenomenon was repeated 

 several times. Cirrostrati as well as cirri exhibit very decided 

 luminosity at night. I have often observed the luminosity 

 between the dark cirrostratus bands nearly equal to that of a 

 faint aurora. When the sky is clear during a very high wind, a 

 faint diffused luminosity has been often observed covering the 

 whole sky. The light given out on such occasions is often very 

 considerable. A friend of mine, who was on board a vessel in 

 the Mersey during the memorable storm of the 6-7 January 1839, 

 informs me that he was much struck by the distinctness with 

 which objects were visible during that night. 



IV. Connexion of the Aurora with Cirri and Cirrostrati. 



The cirrus and cirrostratus modifications of cloud have been 

 frequently observed as accompaniments of the aurora. The fol- 

 lowing extracts from my journal, referring to some of the more 

 striking examples of the effect of the aurora on clouds of these 

 types, as well as to certain allied phenomena, will perhaps be of 

 some interest. 



"1840. July 15, ll h p.m. A beautiful luminous appearance 

 in N. and N.E. arising from cirri in that direction. Light very 

 uniform, and as vivid as that of an average aurora. It had a 

 sort of phosphorescent appearance. 



"Aug. 19. Cirrous bands N. to S., moving briskly from W. 

 It was very interesting to see the alternating bands keep distinct 

 without mingling, although impelled by a considerable current. 

 The bands seemed to act upon each other with a repulsive force. 



" Sept. 5, 9 h p.m. Clear. Some streaky semi-luminous 

 masses of vapour resembling cirri scattered over the sky, and 

 rendered luminous at intervals by rapid pulsations traversing 

 them instantaneously and showing their full extent and forms. 

 No aurora visible at the time. Next morning, at 7 h , the sky was 

 covered by cirri extending in lines from N.N.W. to S.S.E., and 

 moving slowly from W.S.W. A fine 47° halo surrounded the 

 sun for three or four hours. 



"Sept. 21, 9 h a.m. Pennated cirri, the principal bands ranging 

 N. to S., and the fibres N.N.W. to S.S.E. 



"1841. Jan. 28, ll h 30 m p.m. Wind blowing in gusts from 

 N.W. From the N.N.W. point, dark continuous. cirrous bands 

 extended across the sky to S.S.E. Between the bands through- 

 out their whole extent a very decided luminosity prevailed, of a 

 fine deep yellow tint, like that of the aurora. The luminous 

 bands did not, however, show any tendency to converge to the 

 coronal point, which the streamers of the aurora always do, but 



