378 Proceedings of Philosophical Societies. [Nov 



moon, and from the measurement of terrestrial degrees compared 

 i together at great distances. 



Memoir upon thc^subterrauemis Inundations, to lohich many 

 Quarters of Paris are periodicalli/ exposed ; by M. Girard. — A 

 subterraneous source of water has manifested itself for some 

 months in the northern quarters of Paris, which has produced 

 vm inundation of a great number of cellars, and has spread itself 

 on the surface of some marshes situated below the hospital of 

 St. Louis, between the faubourg of the Temple and the faubourg 

 St. Martin. 



Buache, of the Academy of Sciences, and Bonami, of the 

 Academy of Inscriptions, had already endeavoured to discover 

 the probable cause of similar inundations which were observed 

 in 1740, and renewed in 1788. Perronet was consulted, and in 

 a report made by him to the Prevdt des Marchands, he pointed 

 out the true cause. M. Girard exhibits this cause in a new 

 light, and supports his explanation by facts and reasoning ; so 

 that it admits no longer of any doubt. In 1788, some people 

 attributed these inundations to the reservoir of the steam-engine 

 just established at Chaillot. Lately they accused the basin of 

 la Villette. M. Girard shows with great ease that such causes 

 . as constantly exist cannot serve to explain inundations which 

 arise only after long intervals. In adopting the idea of Perronet, 

 he ascends to the origin of the cause, explains why these inun- 

 dations did not happen before that time, and also shows by what 

 concurrence of circumstances they have been observed to take 

 place three times since 1740. 



Formerly a rivulet which runs from Menil-montant toward 

 Chaillot received the water that drained from Paris and the 

 neighbouring hills. This drain was embanked with walls, and 

 at last arched over. The ground-plot of Paris enlarging, new 

 streets arose upon ground made of rubbish. These buildings 

 prevent the running off of the waters, which, soaking gradually 

 into the earth, raise by degrees the level of the subterranean 

 waters : in very wet years, these waters spread themselves into 

 cellars, which otherwise, by their distance from the rivulet, would 

 appear to be in no danger of such an accident. On consulting 

 the registers of meteorological observations, M. Girard found 

 that in 1786 and 1787 there fell 124 centimetres of rain, and that 

 the rainy days were 324 ; so that in the space of these two years 

 the quantity of rain that fell was one-fifth more than in an 

 average year, and the rainy days were also one-seventh more 

 than usual: hence arose the inundation of 1788. The same 

 ^circumstances took place in 1816 and 1817, and occasioned the 

 inundation of 1818. 



M. Girard, in concluding his memoir, observes, " If it be 

 recollected that these subterranean inundations have hitherto 

 only taken place at intervals of 30 years, and that they have been 



