ZOOLOGY AND BOTANY, MIOROSOOPY, ETC. 919 



Betts describes * Lis examination of samples of butter, in all of which 

 some other fat was present. 



Microscopical Observations on the Constituents of Clouds-f — 

 Herr E. Assmann during a stay of three weeks on the Brocken in 

 November 1884, made some microscopical observations on the con- 

 stituent elements of clouds, which has furnished for the first time a 

 number of what he considers to be exhaustive and reliable facts on the 

 subject. 



On 3rd November at sunrise the Brocken was completely enveloped 

 in cloud, the weather having been very warm, and the mountain clear 

 for several days previously. The higher cloud-line sank however 

 rapidly, and at 7 . 30 Herr Assmann's body was completely enveloped in 

 thick clouds while his head was above them. The surface of this sea of 

 cloud was kept tolerably even by a gentle south wind, portions rising 

 to the height of some metres were driven slowly by the wind. A 

 quarter of an hour later the boundary of the cloud had sunk low 

 enough to leave the highest summit of the Brocken uncovered. This 

 state of things continued throughout the day and the cloud-line 

 remained 5 metres below the summit. 



The Microscope was placed on a rock, a carefully cleaned glass 

 slide used, and observations with direct illumination made with a 

 power of 200. After some time a cloud rose and covered the summit 

 for a space of two metres. Three or four small drops fell on the 

 glass, but evaporated immediately. Others soon appeared, and these 

 it was possible to observe for some time, as the glass had gradually 

 assumed the temperature of the air. Careful measurements, which 

 were considerably facilitated by the use of oblique illumination, gave 

 the following results : — 



The smallest drops of water observed had a diameter of • 014 mm. 

 when spread out on the glass slide. This was the usual size as 

 long as the observations were made near the upper cloud-line ; none 

 were found larger than 0-018 mm. Ten metres lower down the 

 smallest drops were much more rarely found, the predominating size 

 being • 02 mm. ; the clouds were here thick and the sunlight remark- 

 ably diminished. Another observation made 20 metres lower down 

 showed a complete disappearance of the smallest drops. Besides those 

 of 0"02 mm. in diameter, many others were observed of 0*03 mm. 

 After a further descent of 50 metres the lower cloud-line was reached, 

 and here the drops found were of the largest diameter observed, being 

 • 035 mni. In ascending to the former points of observation which 

 had been previously visited, Herr Assmann found generally somewhat 

 larger drops than in descending : at the highest point, however, the 

 smallest drops again predominated. The upper cloud-line did not 

 alter one metre in lieight during the two hours that the observations 

 lasted. The ratio between the height and the diameter of the small 

 drops was calculated by the author at 1 : 12 to 1:8. 



* Micr. Bulletin (Qucf-n'H), ii. (188.5) pp. 23-4. 



t Mf;t<.-orolo;r. Ztitaclir.. ii. (Is8.'5) p. 41. Sec Natiirfyrsclicr, xviii. (1885) 

 pp. l2'J-:',(). 



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