Her father sketched for her a shoulder of mutton sail, and she was rather disappointed when she learned, that the name arose merely from the shape. The conversation was interrupted by the sight of a boat on a river; but it had no sails-it was a ferry boat. At Harry and Lucy's age it was a real pleasure to cross a ferry, though to travellers, more advanced in years, it. may sometimes be a pain, or at least a trouble. They are apt to prefer a bridge. NOTE TO PAGE 314, On Steam Engines. Extract of a Letter to the Author, from u "In estimating the power of steam engines and in steam boats, it would be much more in congruity with powers formerly used, and more magnificent in appearance, if the comparison were made with men rather than with horses. Thus a steam vessel, furnished with two engines, each of fifty horse power, might be stated to have the continual force of fourteen hundred rowers. "I may add, on the subject of steam engines, that we have several working in Cornwall with cylinders ninety inches (7ft. 6 in.) in diameter, and ten feet clear way for the piston. These dimensions, with steam producing an actual power of ten pounds to the inch, give an effect of 636,170 pounds one foot high, which is about half of a good day's work for a strong man. I am not sure whether either of these engines work double; that is, condenses above as well as below the pistons: there cannot be any reason against their being so worked, and they cer tainly might make ten double strokes in a minute. Their effect then in 24 hours, 24 × 60 × 10 × 2 × 636171 (= a day's work), would be equal to the work of fourteen thousand four hundred (14,400) men; and as one horse is equal to about fourteen men, the engine would equal the work of a thousand horses." BO END OF VOL. II. LONDON: |