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Collapse of flues
Collapse of tVlues.--_Experlments on -Projoellers.
89
crete, about 5 ins. in thickness, is first spread out, and on that is applied a layer of bitumen reduced to powder and in a boiling state. On this latter, which is also about 5 ins. in thickness, a quantity of river sand is sifted, and then the surface is pressed down by a heavy cast iron roller, weighing about two tons. In a few hours after, the road thus made may be passed over by the heaviest wagons without the slightest •impressi°n being left by the wheels. The same system is now being applied to part of the Rue St. Honor(~ comprised between the l~alais Royal and the Rue de Richelieu, and in the latter street as far as the end of the Theatre Fran~ais.
Collapse of JFlues. The question of the resistance of thin tubes to collapse has recently occupied the attention of practical men ;-and some important facts, hitherto unremarked, or but partially investigated, have been brought to light. Mr. Fairbairn finds that the intensity of the pressure re. quired to make a flue or other thin tube collapse, is directly as the square of the thickness, nearly inversely as tile diameter, and inversely as the length. The diminution of the strength of a flue, as the length increases, is a law never before, it w~uld appear, suspected. For computing the pressure in pounds on the square inch which a wrought iron flue can sustain, the following rule is sufficiently near the truth for practical purposes :'---Multiply the constant factor 806,000 by the square of the thickness, in inches; and divide b y the product of the length in feet, and diameter-in inches. It is of great importance to strength that the flue should be as c2¢lindrical as possible.--iondon Artizan, _Dec., 1858.
Experiments on -Propellers. In a former number of the Journal, we described a new propeller invented by Lieut. Vergne, the characteristic of which was the fluting or ribbing, of the surface (3"ourn. Pr. Inst., 3d Series, vol. xxxv., page 299). At the meeting of the Paris Academy of Sciences, 25th of October, 1858, M. Clapeyron presented the results of some experiments made with it. JExperiments on Le Vigilant.--The mean economy of fuel showed a gain in favor of the Vergne propeller of 17 per cent. The velocity was greater by more than half a knot, or 6 per cent. The new propeller turns more easily. The disturbance of the water near the stern disappeared; the wake was.as smooth as that of a sailing vessel, and the whirlpool from the propeller appeared only at a distance of 7 or 8 metres astern. _Experiment on .L'Austerlitz, reported by Lieut. Zoyer.--With the former propeller the engines gave but 42 turns ; the shaking disordered 8*
89
crete, about 5 ins. in thickness, is first spread out, and on that is applied a layer of bitumen reduced to powder and in a boiling state. On this latter, which is also about 5 ins. in thickness, a quantity of river sand is sifted, and then the surface is pressed down by a heavy cast iron roller, weighing about two tons. In a few hours after, the road thus made may be passed over by the heaviest wagons without the slightest •impressi°n being left by the wheels. The same system is now being applied to part of the Rue St. Honor(~ comprised between the l~alais Royal and the Rue de Richelieu, and in the latter street as far as the end of the Theatre Fran~ais.
Collapse of JFlues. The question of the resistance of thin tubes to collapse has recently occupied the attention of practical men ;-and some important facts, hitherto unremarked, or but partially investigated, have been brought to light. Mr. Fairbairn finds that the intensity of the pressure re. quired to make a flue or other thin tube collapse, is directly as the square of the thickness, nearly inversely as tile diameter, and inversely as the length. The diminution of the strength of a flue, as the length increases, is a law never before, it w~uld appear, suspected. For computing the pressure in pounds on the square inch which a wrought iron flue can sustain, the following rule is sufficiently near the truth for practical purposes :'---Multiply the constant factor 806,000 by the square of the thickness, in inches; and divide b y the product of the length in feet, and diameter-in inches. It is of great importance to strength that the flue should be as c2¢lindrical as possible.--iondon Artizan, _Dec., 1858.
Experiments on -Propellers. In a former number of the Journal, we described a new propeller invented by Lieut. Vergne, the characteristic of which was the fluting or ribbing, of the surface (3"ourn. Pr. Inst., 3d Series, vol. xxxv., page 299). At the meeting of the Paris Academy of Sciences, 25th of October, 1858, M. Clapeyron presented the results of some experiments made with it. JExperiments on Le Vigilant.--The mean economy of fuel showed a gain in favor of the Vergne propeller of 17 per cent. The velocity was greater by more than half a knot, or 6 per cent. The new propeller turns more easily. The disturbance of the water near the stern disappeared; the wake was.as smooth as that of a sailing vessel, and the whirlpool from the propeller appeared only at a distance of 7 or 8 metres astern. _Experiment on .L'Austerlitz, reported by Lieut. Zoyer.--With the former propeller the engines gave but 42 turns ; the shaking disordered 8*