OVER A WIDE EXP ANSE IN FRANCE. 97 



" It was long believed that this difference was owing to this — ^that 

 the drops of rain increased in bulk by aggregation during their fall ; 

 it is agreed now that the relatively lesser amount collected in 

 the pluviometre on the terrace is attributable to atmospheric eddies. 

 But, if it be so, the topographical modifications to which the vicinity 

 and approaches to the Observatoire have been subjected since 1688 

 may suffice perhaps to explain the augmentation of the actual means. 

 This idea natm-ally suggests itself when astronomers are heard com- 

 plaining that, in consequence of the multiplication of street carriages 

 and other conveyances, of gas lights and of hells, certain researches 

 have become impossible in the Observatoire of Paris, so that it is 

 necessary to remove it to the country, and it is imperatively 

 necessary to decentralize the study of astronomy. 



" In short, it may be admitted in regard to Paris, that if the 

 rainfall be different from what it was during the last century, the 

 variation is so inconsidei*able that doubts are entertained as to what 

 the character of the variation is." 



Similar comments are made on observations made at Bourdeaux. 



" The observations which we possess for the city of Bourdeaux are 

 summarised in the following table, the numbers given in which are 

 taken, in like manner, from the valuable collection of M. Raulin : — 



TABLE OF MEAN ANNUAL RAIN-FALLS AT BOURDEAUX, IN DECADES. 

 Periods. Number of Years. Rain-fall. Difference. Names of the Obserrers. 



1714-1720 7 659-1 ] 



1721-1730 10 737-5+ 78-4 | 



1731-1740 10 735-1- 2-4 I ^^ - ,, 



1741-1750 10 693-6- 41-5 \ ^'^'"^^^^^^ ^'^^^^^ ^^^ s^"' 



1751-1760 10 670-0- 23-6 | 



1761-1770 10 647-8- 22-2 J 



1842-1850 8 .849-2 + 207-3 ) 



1851-1860 10 795-2 - 54-8 / 



1776-1786 10 641-9- 5-9 Guyot and De la Mothe. 



Abria. 



1851-1860 10 820 Petit-Laffitte. 



General average, 719 millimetres. 



" The column of differences here shows still that the variations do 

 not follow a law of continuity. For the first series of 67 years the 

 annual mean is 684-7 millimetres, while for the new series, 

 1842-1860, this mean rises to 820, an augmentation of 20%. 



H 



