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Laws of friction
Laws of F~'ivlion.
285
attack. If these simple receipts for the prevention and cure of a terrible complaint, are supported by further experience, M. G. will have rendered a great service to many usefid and laborious classes of manufacturers and artists. ~lbid.
Prizes awarded by the Society for the Encouragement of National I'iulustry. On the £Sth December the Society for the Encouragement of INational Industry held its public semi-annual meeting for the year 1831. Of twenty-one competitors for the prize offered tbr the best means of security against tile explosions of steam boilers, and for such a form of boiler as would guard against the etti~cts of such explosions, no one obtained the prize. Silver medals were awarded to the following persons--M, ltall, of Paris, tbr a combined safety valve and fusible plate: M. Roux, for a new kind of feeding pump ; and M. Trimot, engineer and maker of steam engines~ for his water gauge tube, and tiasible plate applied to the boiler. [Ibid.
Laws of Friction. Notwithstanding the ability of Coulomb, and the care which he bestowed upon all his experiments, his researches upon the subject offi'iction, the results of' which are given in the memoirs of the French academy for t785,were incomplete, and, in some respects, eontradietory~ and theiraceuracy has been, in consequence, suspected. The researches since made upon the same subject by Rennie,Winee, and others, have neither been sufficiently extensive nor precise to set the question at rest. Mr. Morin, by means of an apparatus better calculated tbr giving precise results than that of Coulomb, has lately made a new set of experiments, varying the velocity from the lowest up to ten feet and upwards a second. T h e rubbing surfaces also varied from some tenths of a square inch to nearly five hundred square inches, and tile pressures from ninety pounds to o~000 lbs., and were carried even as high as ~500 lbs. All the experiments made within these limits agree in showing that the friction of surfaces moving on each other, is independent both of the velocity and the surface, and proportional to the pressure. Coulomb, it is true, had ah'eady inferred these laws, but he stated many exceptions~ to them, which, according to the present researches, do not exist. Coulomb supposed that in the case of oak moving over oak, tile grain of tile wood all running t!~e s a t e way and in tile direction of the motion, the relation of friction o pressure was 11 p e r cent., while Mr. Morin found it to be 48 and 3~. Mr. Morin found for elm running over oak 48, when the fibres are parallel, and 4i when they are perpendicular. He also rectifies the mistake of mechanics who-believe the friction to be less between heterogenous substances than between those of the same kind~ and
286
Compensating Pendulums--Preservation of lUood.
shows that the friction of metals on wood is greater than that of oak on oak ; thus when iron is made to move over oak, the ratio is .61; and in the case of copper over the same wood, the ,-atio rises to .6~. These interesting exl)eriments, a report ut)on which is to be made to the academy by Messrs. Poisson, Arago, and Navier, will be continued by the author, who intends to obtain~ if it be possible, tile coefficient of friction lbr all the materials employed in the mechanic arts~ in building, &e. [./lcademy of Sciences~ 1~ Dee.
Compensating Pendulums. After the pendulum was applied as a regulator to cloeks~ and tile other paris of these instruments had been rendered t)erfect in theic construction, so great a regularity was obtained that the variations caused by the expansion and contraction of the rod of the pendulum, became sensible. M. tlenry Robert, clockmaker at the palais royal, and pupil of Braguet~ has lately communicated to the Society for the Encouragement of National Industry, a more simple metlmd than t h a t in use tbr obtaining an exact compensation in pendulums beating th~ half second. The commma method of compensation is to make t h e rod ofihe half second pendulum of a single platinum tube, anti t h e bob of zinc; the difli~rence in the expansions of these two metals is suclb that by exact calculations a perfect correction is obtained. Robert directed his attention to the pendulum with a wooden rod, for tile purpose of using it in ornamental time pieces, for which t h e zinc and platinum pendulum (gridiron) was unsuited, fi'om the c o m parative plainness of its appearance. By a simple and easy device h e has so constructed it as to protect it completely from the action o f the atmosphere, so that it may now be substituted Ior the best metallic compensators, in every kind of clock. In tile construction of tiffs new pendulum, M. R. profiting, on the one hand, by the well k n o w n property possessed by the wood of the fir tree, of preserving i t s length unaltered in all changes of temperature, has been enabled t o confine his attention simply to its tendency to warp, by tile a b stwption of moisture from tile atmospher% and to prevent this enclose.~ the rod made of this wood in a metal box~ the expansion of the b o b corrects that of the tube. 'l?bis simple pendulum unites all the requisites of a good compens~for, while at the same time it may be put together with ease ; it t a k e s tql little room, is of a very simple form, anti may be placed in t h ~ most beautiful models where the pendulum is exposed to view.
Elbid.
Preservation of l~Vood. A method of preserving buildin~ timber from decay has long beet-~ a desideratu u.
The atteml)tS Ii~therto mad% have no b h o w e v e r ,
285
attack. If these simple receipts for the prevention and cure of a terrible complaint, are supported by further experience, M. G. will have rendered a great service to many usefid and laborious classes of manufacturers and artists. ~lbid.
Prizes awarded by the Society for the Encouragement of National I'iulustry. On the £Sth December the Society for the Encouragement of INational Industry held its public semi-annual meeting for the year 1831. Of twenty-one competitors for the prize offered tbr the best means of security against tile explosions of steam boilers, and for such a form of boiler as would guard against the etti~cts of such explosions, no one obtained the prize. Silver medals were awarded to the following persons--M, ltall, of Paris, tbr a combined safety valve and fusible plate: M. Roux, for a new kind of feeding pump ; and M. Trimot, engineer and maker of steam engines~ for his water gauge tube, and tiasible plate applied to the boiler. [Ibid.
Laws of Friction. Notwithstanding the ability of Coulomb, and the care which he bestowed upon all his experiments, his researches upon the subject offi'iction, the results of' which are given in the memoirs of the French academy for t785,were incomplete, and, in some respects, eontradietory~ and theiraceuracy has been, in consequence, suspected. The researches since made upon the same subject by Rennie,Winee, and others, have neither been sufficiently extensive nor precise to set the question at rest. Mr. Morin, by means of an apparatus better calculated tbr giving precise results than that of Coulomb, has lately made a new set of experiments, varying the velocity from the lowest up to ten feet and upwards a second. T h e rubbing surfaces also varied from some tenths of a square inch to nearly five hundred square inches, and tile pressures from ninety pounds to o~000 lbs., and were carried even as high as ~500 lbs. All the experiments made within these limits agree in showing that the friction of surfaces moving on each other, is independent both of the velocity and the surface, and proportional to the pressure. Coulomb, it is true, had ah'eady inferred these laws, but he stated many exceptions~ to them, which, according to the present researches, do not exist. Coulomb supposed that in the case of oak moving over oak, tile grain of tile wood all running t!~e s a t e way and in tile direction of the motion, the relation of friction o pressure was 11 p e r cent., while Mr. Morin found it to be 48 and 3~. Mr. Morin found for elm running over oak 48, when the fibres are parallel, and 4i when they are perpendicular. He also rectifies the mistake of mechanics who-believe the friction to be less between heterogenous substances than between those of the same kind~ and
286
Compensating Pendulums--Preservation of lUood.
shows that the friction of metals on wood is greater than that of oak on oak ; thus when iron is made to move over oak, the ratio is .61; and in the case of copper over the same wood, the ,-atio rises to .6~. These interesting exl)eriments, a report ut)on which is to be made to the academy by Messrs. Poisson, Arago, and Navier, will be continued by the author, who intends to obtain~ if it be possible, tile coefficient of friction lbr all the materials employed in the mechanic arts~ in building, &e. [./lcademy of Sciences~ 1~ Dee.
Compensating Pendulums. After the pendulum was applied as a regulator to cloeks~ and tile other paris of these instruments had been rendered t)erfect in theic construction, so great a regularity was obtained that the variations caused by the expansion and contraction of the rod of the pendulum, became sensible. M. tlenry Robert, clockmaker at the palais royal, and pupil of Braguet~ has lately communicated to the Society for the Encouragement of National Industry, a more simple metlmd than t h a t in use tbr obtaining an exact compensation in pendulums beating th~ half second. The commma method of compensation is to make t h e rod ofihe half second pendulum of a single platinum tube, anti t h e bob of zinc; the difli~rence in the expansions of these two metals is suclb that by exact calculations a perfect correction is obtained. Robert directed his attention to the pendulum with a wooden rod, for tile purpose of using it in ornamental time pieces, for which t h e zinc and platinum pendulum (gridiron) was unsuited, fi'om the c o m parative plainness of its appearance. By a simple and easy device h e has so constructed it as to protect it completely from the action o f the atmosphere, so that it may now be substituted Ior the best metallic compensators, in every kind of clock. In tile construction of tiffs new pendulum, M. R. profiting, on the one hand, by the well k n o w n property possessed by the wood of the fir tree, of preserving i t s length unaltered in all changes of temperature, has been enabled t o confine his attention simply to its tendency to warp, by tile a b stwption of moisture from tile atmospher% and to prevent this enclose.~ the rod made of this wood in a metal box~ the expansion of the b o b corrects that of the tube. 'l?bis simple pendulum unites all the requisites of a good compens~for, while at the same time it may be put together with ease ; it t a k e s tql little room, is of a very simple form, anti may be placed in t h ~ most beautiful models where the pendulum is exposed to view.
Elbid.
Preservation of l~Vood. A method of preserving buildin~ timber from decay has long beet-~ a desideratu u.
The atteml)tS Ii~therto mad% have no b h o w e v e r ,