PROGRESS OF METEOROLOGY IN 1889. 239 



In a brief discussion of the relations of forests to raiii-fall, three cases 

 are adduced all of \ybich contirin the view that the forests have increased 

 the rain-fall, but the evidence is stated to be in no case absolutely con- 

 clusive. 



The remaining portion of the memoir is occupied with the considera- 

 tion of the questions as to whether any laws of coincidence or sequence 

 can be derived ; whether certain regions are, as a rule, subject simultane- 

 ously to similar or alternative conditions, whether any physical connec- 

 tion can be traced between abnormal meteorological conditions in a 

 given region and the excess or deficiency of rain-fall there or elsewhere, 

 and whether there are valid reasons for believing that the rain-fall of 

 India is subject to any periodic law. 



Divrnal period of rain-fall at Caloutfa. — Mr. H. F* Blanfordhas found 

 the following times of maximum and minimum in the daily period of 

 rain at Calcutta. In the cold season (November to February) the prin- 

 cipal minimum occurs at noonday, the maximum from 6 to 9 p. m.; in the 

 hot season (March to May) there Is only one well defined maximum and 

 minimum, the former falling from G to 8 P. M., the latter between sunrise 

 and 11 A. M, In the rainy season the principal maximum occurs from 

 2 to 4 p. M., and the principal minimum a little before 11 A. M. The 

 daily period in the amonnt of rain agrees, in general, with the period 

 of rain frequency. {Indian Meteor. Memoirs^ IV, pp. 39-4G.) 



Diurnal per iod of rain fall. — Dr. Hfllmann has reported to the German 

 Meteorological Society some of the results of his investigations upon 

 the daily period of i)recipitation. He shows that the different curves 

 may be reduced to types which are characteristic of certain localities 

 and seasons. The afternoon nuiximum prominent in many places may 

 be shown to rise naturally' from the daily ])eriod of thunder-storms, 

 whilst the equally widely extended nocturnal maximum, which is es- 

 pecially prominent in winter, and in all seasons on the west coast of 

 Europe, appears to be connected with certain peculiarities in the daily 

 period of air pressure, temperature, and wind velocity. {Meteorolo- 

 (fische Zeitschrift, 1889, vi, p. 271.) 



Diurnal periodicity of rain-fall at Hong Kong. — In the rainy season, 

 from June to August, the diurnal variation is most strongly marked. 

 The rain curves then run from a forenoon maximum at 9 A. M. to an 

 evening minimum at 11 P. m. From March to May, the principal maxi- 

 mum falls at noon and the principal minimum at 7 P. m. In autumn 

 and winter the diurnal curve is quite irregular. {Ibid., p. 350.) 



Ifaily period of rainfall at Vienna. — The general results of the self- 

 recording rainfall observations for seven years at Vienna have been 

 worked out by Ilann. When given in groups of two months each no 

 regular diurnal period is manifest, but in the total of seven months 

 from April to October a periodicity is clearly expressed. The princi- 

 pal maximum of both frequency and quantity of rain occurs at the hour 



