78 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



tion of the ordinary clouds of the atmosphere ; but however 

 beautiful the analogy between the appearances may be, yet 

 the physical explanations are not likely to be so similar. 



In the annual reports for 1876 and 1877 of the Chief of 

 Engineers, Mr. O. B. Wheeler gives a valuable reduction of 

 all the observations of changes in level of the great lakes. 



Dr. E. Purkyne contributes a very interesting paper on the 

 rainfall at Santa Cruz. The author gives some account of the 

 early condition of the forests, and of the droughts to which 

 the island is subject. There is no evidence of any great 

 change of climate or of the dependence of rainfall upon for- 

 ests, but rather upon the presence of hills and the position 

 of the water and land relative to the winds. 



Dr. Ilellmann has carefully studied the summer rainfall in 

 Germany, using ten-day means for 22 years. He finds a 

 double maximum in frequency and quantity the first in 

 June, the second in August. The cold period of June ends 

 the first rain period, and is due to the irruption of cold air 

 from the northwest. 



Dr. Von Bebber (Munich, 1877) has collected a large quan- 

 tity of data relative to the rainfall of Germany. He finds 

 the average in all Germany to be 71 centimeters. The 

 influence of altitude is to increase the rainfall upon such 

 mountain-tops (up to 1200 meters) as were available. A 

 similar distribution prevails in America on Mt. Washington, 

 and in India on the windward side of the mountain-ranges, 

 all which, by causing the winds to pnsh the air upward, de- 

 termine the resulting condensation. 



Rubensen gives (K. SvenskVet. p. 13,1876) the geograph- 

 ical distribution of rain in Sweden. The rainfall is heaviest 

 (700-800 mm.) in Southwest Sweden, and least on the east 

 side of the Scandinavian Mountains. 



As to the manner in which raindrops and hailstones are 

 formed, Professor Osborne Reynolds maintains that there 

 are in a cloud large and small particles of water and ice, and 

 that of these the larger ones have demonstrably the greater 

 velocity of fall; they will, therefore, overtake the smaller ones 

 and add them to their own mass. These larger particles are 

 most numerous at the upper surface of a cloud, where the 

 cooling due to radiation takes place most rapidly. Beyond 

 a certain limit raindrops cannot grow, as they will break up 



