1819.] Royal Academy of Sciences. 379 



occasioned by circumstances absolutely similar in themselves, it 

 may be concluded that this accident will seldom occur ; for it 

 depends not only on the excessive quantity of rain, but also on 

 its continuance. This much is certain, that on account of the 

 obstacles which have been at different times put in the way to 

 prevent the free drainage of the rain water in the northern quar- 

 ters of Paris, every time the depth of rain that falls in the space 

 of two vears shall be greater than 120 centimetres, and the num- 

 ber of rainy days in that interval shall be more than 320, those 

 quarters of Paris which are situated on the right bank of the 

 Seine will have reason to expect a subterraneous inundation the 

 next year." 



Memoir on the Topography and Levelling of Paris ; by M. 

 Guard. — The three islands formed by the Seine, and the quarters 

 extending to the north and south, were formerly meadows, 

 which were overflowed by the Seine every time that there hap- 

 pened a flood. The gravel carried by the stream, and the mud 

 which was suspended in the water, were deposited on the surface 

 of the meadows. Every year a new layer of these deposits 

 raised the soil, while at the same time similar depositions also 

 elevated the bed of the river. As the valley became peopled, 

 the necessity of preventing these inundations obliged the inhabi- 

 tants to accelerate the operations of nature by bringing fresh 

 earth, or to raise dikes or quays upon the shores of the river, 

 which might prevent these overflowings; and the bed of the 

 Seine being continually elevated, the quays were forced to be 

 frequently raised, and the surface of different quarters heightened 

 artificially. The rubbish carried out of the inhabited part formed 

 in time the rising grounds of Moulins, and of Notre Dame de 

 bonne Nouvelle, the small hills of rue Hyacinthe, rue Taranne, 

 and the labyrinth of the Jardin des Plantes. The population 

 increasing, the surfaces of these deposits of rubbish were partially 

 levelled, and new streets traced upon them. The Boulevards 

 towards the north, being the remains of the ancient ramparts, 

 form a spot of ground which is higher than the rest of the city 

 and neighbouring fauxbourgs. 



It has been long proposed to determine the real level of the 

 different quarters. In 1742, Buache formed the project of per- 

 forming a hydrographical plan of Paris. The inundation of 1740 

 furnished the original data of a general level of the quarters that 

 had been laid under water. He afterwards drew several profiles 

 of the ground, by traversing the town in different directions. 

 This work is the only one hitherto published. In order to begin 

 a new work upon a larger scale, there were traced upon Ver- 

 nique's large plan the heights of different points of the surface, 

 in reference to ahorizontal plane raised about 7(J metres above 

 the lowest level of the Seine. After having carefully verified 

 these primary positions, successive additions were made, and 



