80 Scientific Intelligence. 



at once distinguished. For if common cirrus-clouds are within 

 the twilight segment, when the sun is 10° or more below the 

 horizon, they are always darker than the twilight-sky around 

 them ; while, on the other hand, the luminous night-clouds are 

 always brighter than this sky. Moreover, the ordinary cirrus- 

 clouds do not usually disappear, when the twilight-arch passes by 

 them so that they are left in the night-sky ; they only change 

 their aspect in such wise that, whereas they were previously 

 darker than the sky around them, they appear, after their entrance 

 into the night sky, brighter than this is. But the luminous night- 

 clouds disappear entirely so soon as the twilight-arch has moved 

 past them, and only such portion remains visible as remains 

 within the twilight-segment. With regard to the color of the 

 luminous night-clouds, it should be mentioned that they glow 

 with a white and silvery luster, which changes toward a golden 

 yellow in the vicinity of the horizon. And furthermore, it is 

 worthy of notice, that the phenomenon is not manifested on every 

 otherwise cloudless evening or morning during the season of its 

 visibility, but occurs for the most part with intervals of from 8 

 to 14 days, and then usually remains visible for several succes- 

 sive nights. For observing it, it is requisite that the horizon in 

 the direction of the twilight be as free as possible. Electric and 

 gas-light generally interfere with its perceptibility. 



2. American Association for the Advancement of Science. — 

 The next meeting of this Association will open at Toronto, Canada 

 on Tuesday the 27th of August. The prospectus of the meeting 

 states that the Queen's Hotel will be the hotel headquarters of 

 the Association. The first general session will take place on 

 Wednesday, the 28th at ten o'clock in the Convocation Hall, 

 University Buildings. The address of the retiring President, 

 Major J. W. Powell, will be delivered Wednesday evening. 



The President of the meeting, is Prof. T. C. Mendenhall of 

 Indiana. 



For all matters pertaining to membership papers and business 

 of the Association, the Permanent Secretary, Prof. F. W. Put- 

 nam, should be addressed at Salem up to August 22, and after 

 that time to Toronto, A. A. A. S. A circular will soon be is- 

 sued by the Local Committee, of which C. Carpmael, Esq , is 

 President, and Prof. J. Loudon, Local Secretary. 



The meeting of the American Geological Society is to be held 

 at Toronto on the 28th and 29th of August, as mentioned on p. 

 503 of the last volume of this Journal. The Entomological Club 

 will meet at 9 a. m., on Wednesday, July 28, and the Botanical 

 Club, on Tuesday, Aug. 27. 



3. Sir Wm. Dawson on New Erian plant , p. I. — Explanation 

 of figure. — Dictyo-cordaites Lacoi, much reduced, (a) Venation 

 of leaf, natural size, (b) Fruit enlarged. 



