138 INTRODUCTION. 



finally an uniform course of a quarter of an inch in thickness over the whole, in 

 front of which the brick facing was laid up. A course of plastering was also put 

 over the roofing arch. The concrete masonry was formed by mixing one part 

 hydraulic cement, three parts clean sand, and three parts fine broken stone. 

 The masonry was all laid up in hydraulic cement. The mortar for the stone 

 work was composed of one measure of cement to one of clean sharp sand ; and 

 that for the brick and plastering consisted of one part of cement to two of sand. 

 The area of a cross section of the masonry is, 



Concrete masonry, 4,605 square feet. 



Stone inside walls, 21,572 " 



Do in spandrels, 2,690 " 



28,867 



Brick in arches and side facing, 13,658 square feet. 



Total, 42,525 " 



In embankment the concrete masonry is laid on foundation walls, has one foot 

 extra thickness and three feet in extra width. The base of the side walls is also 

 increased, and the proportion of cement to sand in concrete and mortar for stone 

 work, is 1 to 2j feet. 



The proportion of embankment to excavation on the line of the aqueduct, is 

 about as one to eight. The aqueduct is covered with earth of sufficient depth to 

 protect it from frost. To pass streams, there are one hundred and fourteen cul- 

 verts, the aggregate length of which is 7,959 feet, and varying in span from 

 1J feet to 25 feet. There are five road culverts from 1 to 20 feet span. All 

 the culverts are constructed in the most improved manner, laid in hydraulic 

 cement. 



There are thirty-three ventilators, to give free circulation of air through the 

 aqueduct. They rise fourteen feet above the surface of the ground, tapering 

 towards the top, and are of circular form, constructed of well dressed stone, and 

 have an aperture of fifteen inches in diameter : they are placed at a distance 

 from each other of one mile. 



There are six waste-weirs, constructed of well dressed stone, having cast-iron 



