OVER A WTPF. EXPANSE, 95 



betake ourselves to the records of the rainfall and enquire whether 

 either of these two conflicting assertions have any value. 



" In France, the earliest series of pkiviometric observations is that 

 of r Observatoire. It was begun in 1689 by Phillippe de la Hire, in 

 accordance with an express order given by Colbert to the Academy, 

 in view of the requirements of the hydraulic works at Versailles, to 

 ascertain what quantity of water the rain falling on the plains around 

 could supply to the projected reservoirs. 



" It has been repeatedly interrupted, and again resumed. And 

 a summary of the record is given in the following table, taken 

 from a valuable collection of pluviometric observations publi shed 

 by M. Raulin, Professor of Geology in the Faculty of Sciences at 

 Bourdeaux : — * 



TABLE OF MEAN ANNUAL RAINFALLS IN DECADES, ACCORDING TO THE 

 rLUVIOMETRB ON THE TERRACE OF THE OBSERVATORY AT PARIS. 

 Periods. Number of Years. Rainfall. Difference. Names of the Observers. 



1688-1700 10 517- ) 



1701-1710 10 480-6- 36-4 V Lahire, 1688 to 1718. 



1711-1720 10 464-9- 15-7 j 



1721-1730 10 378-3- 86-6),, ia- n a- a t? u 



1731-1740 10 411- + 327lM^rald,^ran^J7.^,d/F^^^^ 



1741-1750 10 425-5+ 11-5 j 1709 to 1.54. 



1773-1780 8 537-6 + 114-1). * ai t> ^ ittq 



i^oi ^'•ar\ in nnr n qo t ' Jeaurat, Alex. Bouvard, 1773- 

 u81-l<90 10 506-9- 32-/ V ' ,^^,0 



1791-1798 8 413-7- 93-2 j ^''^^• 



1804-1810 7 518-3 + 104-6] 



1811-1820 10 496-5- 21-8 | 



1821-1830 10 498-6+ 2-1 | ^^ , , t ^r • 



1831-1840 10 509-3+ 10-7 Bouvard, Arago, Le Verrier. 



1841-1850 10 529-3+ 20- 



1851-1860 10 520-3- 9- J 



" The column of difference shows that the variation followed no law 

 of continuity. The long-continued series of observations presents us 

 with three separate periods, and these give respectively for the annual 

 mean, during 65 years, 1688 to 1754, 448-6 millimetres; 26 years, 

 1773 to 1798, 489-6; 57 years, 1803 to 1860, 512-0. 



" Many authors have appealed to these numbers to prove that the 

 rainfall in Paris is now [not less, but] greater than formerly; but this 

 has been met by the following considerations : In pluviometric observa- 



* Bourdeaux, Chaumas. 1864. 



