7^4 PHILOSOPHICAL TRANSACTIONS. [aNNO 1672. 



liigh. The second, to be more raised, is 3 fathoms thick, and 25 fathoms high: 

 it stands very near the midst of the causey, 33 fathoms distant from the first. 

 The third, which makes the foot of the causey, and is 31 fathoms off from the 

 second, is 8 feet thick, and 15 fathoms high. Tlie empty space between the first 

 and second wall, is to be filled with stones and earth well rammed together and 

 made even, so that it may be covered with a bed of loam 6 feet thick, sloping, 

 and insensibly descending from the second to the first wall, so that the water, 

 which will be made to swell to the height of 20 to 25 fathoms, spreading itself 

 upon this glacis or slope, and to lean every where on its centre, may not spoil 

 the causey. In the like manner is to be filled up the empty space between the 

 second and third wall, descending also slopewise from the second to the third, to 

 serve for a buttress to the second, that is to bear all the weight and force of the 

 water. 



All these walls, and even those of the gallery, are to be counter-walled by a 

 wall of 2 feet thickness. Besides, the gallery is to be counter- vaulted by an- 

 other vault; and the intermediate empty spaces are to be done up with a clayey 

 earth well rammed; that so, in case that by any extraordinary accident the 

 water should come to make any gap in the loam-bed, that is between the first 

 and second wall, the rest may by this means be preserved entire. 



In the first wall there are stones in toothings from the top to the bottom, on 

 the right and left of the aqueduct's mouth, and of the galleries window : and 

 this is to make a cavity chamber-wise, 4 feet square. The wall of this little 

 structure is to be 6 feet thick, counter-walled with another wall 2 feet 

 thick, with a loam-bed between, to keep it safe. It shall end on the 

 top above the gallery slopewise and like a vault, which is likewise to be 

 counter- walled and counter- vaulted, with clay between. This walled square 

 cavity is to be pierced by six or seven metal pipes, as large as those of cannons, 

 and have their orifices from without ; thereby to receive the water of the maga- 

 zine to the height of the gallery. The cocks are to be within, shut up in the 

 little space that the said cavity is to contain, to cast the water down so as it may 

 have a fall of 4 fathoms. These cocks shall be opened through a window that is 

 at the end of the gallery. And there is to be yet another little aperture beneath, 

 at which one may descend into this chamber, in case the passage of the water 

 shall be incumbered, or that any other inconvenience is to be remedied. For 

 which purpose there shall be fastened eight bars of iron in the walls like a kind 

 of stairs, for the conveniency of those that shall go down. 



This gallery is only to serve for passing to open the cocks, according as there 

 shall be need of water : and the water falling down will find issue through the 

 aqueduct, following the bed of the rivulet Audot, falling into the jderiving chan- 

 nel below the village Vaudreuil. 



