Ice 3 inches thick, will bear infantry marching in file; from 4½ to 6½ inches, cavalry and light artillery; and beyond that the heaviest gun carriages may pass in safety. Ice 8 inches thick will bear nearly 10 cwt. upon a square foot without danger.
34. How is the size of a rope designated?
By its circumference: thus, a two-inch rope is a rope two inches in circumference.
35. How is the strength of a hemp rope, or the weight it will support, ascertained?
Square the circumference in inches, and divide by 5, for the weight in tons, that it will bear suspended from it.
36. How can the breadth of a river be ascertained without instruments?
As follows:
157]
Fig. 6.