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[[page number]] 121

[[margin note:  Wheel & pinion fixed nearest the middle of their arbor are best.]]

   He remarks first, that a watch wheel placed near the middle of its arbor is in the most advantageous position, especially if its pinion be nearly in the same position; because, then the effort it receives, is distributed equally between the two pivots;  the pivot holes in the two plates, will wear equally, and on the same side, and their enlargement will always let the wheel continue parallel to the plates: The consequence will be, that the positions of the planes of the wheels, suffering no alteration by such wearing, with respect to one another, they drive one another on without any alteration, as to the pitching, or the friction.

[[margin note:  A contrary case.]]
   But the case will be otherwise, when the wheel or the pinion are near one of the extremities of the arbor, as the friction arising from the action of the wheel, is no longer equal on both the pivots; that which is nearest the pinion, receives almost the whole effort of the preceding wheel, whilst the other is effected with it in a very slight degree only.  It must thence follow, that the hold of such pivot must wear much more, and that in a shorter time, than the other;
[[margin note:  And the disorder thence arising]]
whence must be produced a disorder, as to the justness of the watch: And yet this is not the worst consequence to be apprehended; one of the holes cannot wear, or be enlarged more than the other, without altering the position of the arbor, and consequently that of the parallelism of the plane of the wheels; whence it follows, that the pitching must be absolutely altered, and the watch lose much of its justness.

[[margin note:  Position of the fusee hinders a correction]]
   This is the great defect of common watches; the pinion of the small middle wheel, or the third wheel M (in Fig.27.) and that of the contrat wheel r are so near one of their pivots, that it is very frequently necessary to stop or bush up their holes & drill them a new in a year or two.  M. [[underline]] le Roy [[underline]] set himself about remedying this mischief for several years; but the situation of the fusee was an obstacle to his placing the little middle wheel as it ought to be.  The fusee is a kind of truncate cone, much wider at the base than the top, and is raised the higher by the fusee wheel at bottom; in so much, that at about half the distance between the two plates, it is impossible for the small middle wheel to have its requisite diameter, without placing it at the top of its arbor, and its pinion at the bottom of the same.

[[margin note:  Yet remedied by inverting the fusee.]]

   To remedy this inconvenience, M [[underline]] le Roy [[underline]] at last thought of inverting the fusee, so that the wide base should be at top, and little end at bottom, near the great wheel; for the main thing to be done was to Cover the little middle wheel in the frame, and the inversion of the fusee being once put in practice, the obstacle no longer subsisted.  The little middle wheel being thus  [[e?]] raised to a sufficient height, might act upon the pinion of the contrat wheel, near the middle of its arbor; and this upon trial, perfectly answered the purpose of the artist.

[[margin note:  New positions of the wheels.]]
   
   In fig.28. the fusee is shown inverted at F, the great wheel at G, the little middle wheel at M, a little cap at B.

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