1819.] Days of Rain, Snow, and Drizzle, at Viviers. 113 



at Viviers during 40 years; namely, 16312 lines by 3921, the 

 number of rainy days during that space of time, we obtain 

 4-160 lines for the mean quantity of rain that falls in a day. 

 And if we divide the quantities of rain that fell during each 

 decade by the number of rainy days in that decade, we shall 

 obtain the mean quantity of rain which fell during a day during 

 each decade as in the following table : 



Intensity of diur- 

 nal rain. 



Decades of 

 years. 



Lines. 



1778—1787 4-499 



1788-1797 4-210 



Intensity of diur- 

 nal rain. 



Decades of 

 years. 



Lines. 



1798—1807 3-864 



1808—1817 4-148 



From this, we may conclude that the intensity of the diurnal 

 rain is subject to vary ; for having diminished during the first 

 three decades, it has augmented in the last. 



Finally, if we divide the quantities of rain which fell each 

 month by the number of rainy days corresponding to that month, 

 we shall obtain the mean quantity of diurnal rain during each 

 month as in the following table : 



Lines. 



January 3-447 



February 2*912 



March 2-938 



April 3-551 



May 4-199 



June 4-0dy 



Lines. 



July 3-946 



August 5-690 



September 6*647 



October 5-431 



November 4-641 



December 2*869 



This table gives the ratio of the intensity of the rain. We see 

 that it is greatest in the month of September ; or during that 

 month the greatest quantity of rain falls in the shortest time. 

 Hence it is during this month, or in October, that the great 

 inundations of the torrent of Escoutay take place. This torrent 

 flows into the Rhone, about 250 toises to the north of Viviers. 

 The most violent of its inundations happened on Sept. 2, 1 703, 

 when its waters reached the very gates of the city. The lightest 

 rains are those of the month of December. 



After a lung series of meteorological observations, I find that 

 at Viviers the mean number of serene days in the year is 123 ; 

 of cloudy days, 173 ; of days absolutely overcast, 69 ; of foggy 

 days, 52 ; of snowy days, 5 ; of hail, 3 ; and of thunder, 24. 



Lord Charles Cavendish and Dr. Heberden had remarked 

 (Phil. Trans, vol. lxix) that the quantity of rain which falls upon 

 the same surface at the top of a building is less than at the 

 bottom of it. This fact has just been verified at the Paris obser- 

 vatory with two equal vessels placed, the one on the parapet, and 

 the other in the court. The rain collected in the latter vessel 

 surpassed considerably what was collected in the former. 



Vol. XIV. N° II. H 



