MECHANICS AND USEFUL ARTS. 31 







boat, however, was completed, and is seventy feet in length, twelve feet in 

 width, and when resting upon the water, loaded, displaces about one foot in 

 depth of water. Its upper part is similar to a railroad car, and is warmed by 

 steam. It will accommodate one hundred passengers. It is propelled by an 

 engine acting on a single driving- wheel. Adhesion is given to the wheel by 

 means of penetrating or sharp flanges. Its velocity is controlled by a steam- 

 brake. The runners are so adjusted that it may be made to run through 

 snow five feet deep. The cabin of the boat is twelve by forty feet, and I 

 estimate its weight, when loaded with passengers and freight, at twelve tons. 

 It is my firm conviction that its ordinary speed will be from twenty to forty 

 miles, and on clear, solid ice, its speed may be increased to from forty to 

 eighty." 



THE XAPOLEON DOCKS AT CHERBOURG, FRANCE. 



The naval works at Cherbourg, France, recently, completed by the French 

 Government, after having been in the process of construction for seventy 

 years, at a cost of $15,000,000, are of the most gigantic description. In gen- 

 eral terms, the breakwater may be described as presenting a mass of rubble 

 stone, having a slope, from the bed of the sea to the level, of nearly 22 feet 

 below high-water line of spring tides, towards the roads, in the ratio of one 

 of base to one in height (1 to 1). The top of the mass then has a much more 

 gentle inclination; for, in the width of 19J feet, its inner summit attains the 

 level of 15! feet below high-water line, and there it stops against a wall, 

 almost vertical, rising 7 feet above the same high-water line, or datum. There 

 is a level platform at this height, of 20 feet wide on the eastern arm, and 21 

 feet wide on the western arm; and beyond it there is a solid masonry para- 

 pet (about 5 feet high, and rather more than 8 feet wide) towards the sea. 

 The outer line of this parapet is, in fact, in the continuation of the sea face 

 of the wall, and the latter has been built of coarse and dressed masonry, 

 laid with the greatest care, and composed of the very best materials, upon a 

 general bed of hydraulic concrete, 5 feet thick, laid over the loose rubble 

 hearting. The bottom of the concrete is about 29 feet below datum. Be- 

 yond the edge of the masonry which protects the foot of the vertical wall, 

 the top of the rubble hearting of the breakwater has assumed a slope of 1 in 

 10 towards the open sea, under the influence of storms. This slope contin- 

 ues until the top line has descended to 47 feet below datum, and thence it 

 continues to the bottom, at the rate of U to 1. 



The small materials used in the hearting of the breakwater are naturally 

 exposed to be displaced by storms. Of late, however, a very effectual mode 

 of protecting the sea slope has been adopted, consisting of huge artificial 

 blocks, cubing not less than 26 yards, placed upon those portions of the 

 breakwater which are most exposed to the effects of the sea. These blocks 

 are composed of rubble masonry and of Portland cement mortar. 



Returning, however, to the consideration of the general plan of these 

 offensive and defensive works, we find that there is, at the apex of the angle 

 formed by the meeting of the two branches of the breakwater, a large cen- 

 tral fort, having a total development of about 509 feet, measured on the 

 inner line of the parapet, which forms a very flat semi-ellipse. Behind this 

 battery there is to be raised an elliptical central tower, measuring 225 feet on 

 the major, and 123 feet on the minor axis. A casemated fort, of about 1UO 

 feet front, is to be formed on the western or longer branch, and two large 

 circular forts are placed at the extremities of the breakwater, that of the 



