528 



SCIENTIFIC RECORD FOR 1883. 



masses of fog; 174 clouds of this description were distributed iu alti- 

 tude as sbowu in the following table: (2) As these clouds rise their 

 boundaries become more definite, they assume rounded forms, appear 

 much brighter, and throw deeper shadows; 246 cases of this kind arc 

 given in the accompanying table: (3) Above these latter is a third and 

 very different class ; these are smaller with more delicate illumination and 

 shadows, and are generally arranged in platoons regularly grouped in 

 many ways, sometimes giving the heavens a marbled appearance : (4) Far 

 above these little clouds is a group lying as high up as condensed aqueous 

 vapor is any way visible, and showing the well-known forms of cirrus 

 known as " mare's-tails," "mackerel-sky"; 139 of this class are divided 

 into two groups, the first (4) extending between 9,000 and 18,000, and 

 having a maximum at 13,000 ; the second group (5) extending from 18,000 

 to 33,000 feet, and having a possible maximum of 22,000 feet. These five 

 forms of clouds, and the corresponding altitudes of maximum fre- 

 quency have an interesting relation to the corresponding atmospheric 

 pressures. These latter he has computed by various hypsometric for- 

 mulae with results as given in this table. 



The seventh column in this table gives the average "projected ve- 

 locity" of the movement of the clouds in feet per second deduced by pro- 

 jecting all apparent angular velocities upon a plane surface, separat- 

 ing the middle of each layer. A total of about 900 such observations 

 were available during the first two years. 



Table I. — Fettin's observations of clouds at Berlin. 



Altitude in feet. 



500-1000.. 



1-2,000.. 



2-3,000.. 



3-4,000.. 



4-5,000.. 



5-6,000.. 



6-7,000.. 



7-8,000.. 



8-9, 000 . . 



9-10,000. 

 10-11,000. 

 11,000.... 

 12,000.... 

 13,000.... 

 14,000.... 

 15,000.... 

 16,000.... 

 17,000.... 

 18,000.... 

 19,000.... 

 20,000.... 

 21,000.... 



Frequency by classes. 



27 



107 



35 



5 



II. 







9 



< ; 4 



72 



53 



37 



8 



2 



1 



III. 



(i 

 1 



9 



36 

 34 

 26 



IV. 



9 

 13 



Ki 

 33 

 L3 

 13 



10 

 7 

 3 



Average. 



803 

 1, 455 

 2, 440 

 3, 140 

 4,470 

 5,380 

 6, 500 

 7, 380 

 8,400 

 9, 360 

 10, 200 

 11,500 



12, 300 



13, 300 



14, 300 

 15, 200 

 16, 150 

 17, 800 

 18, 000 

 19, 300 

 20, 000 

 21,300 







920 



585 



335 



228 



185 



143 



144 



115 



112 

 95. 7 

 81.5 

 91.3 

 95. 9 

 84.4 

 92.9 

 51.5 

 60.8 

 44.5 

 61.2 

 91.8 

 27 

 46.3, 



