Oiler . Horologists' term for a small, very short stem in the arbor of a wheel or balance that extends from the point of the pivot to the pinion or wheel, etc. In old French watches, and in almost all the ones made in England at present, these stems are so short that the oil put on the pivots is drawn up onto the pinions or spreads onto the wheels. Among the skilled horologists who noticed this drawback, M. Gaudron was one of the first to venture that if a bottle of oil could be put at each pivot, a watch would stay accurate longer. M. Sully seized the idea and devised little reservoirs (see Règle artificielle du temps , p. 280) that supplied oil to the pivots during evaporation. This method involved a great increase in work and several disadvantages. M. le Roy turned to another expedient, suggested by reading Newton's Optics . Reflecting on the experiment the great man reports on p. 576 of the book just mentioned, M. le Roy reasoned thus: "The pivots are located at the ends of the arbors, the arbors are perpendicular to the plates that support them and meet them at the same point, namely the apex of the angle they form together. Since their arrangement is similar to the mirrors in Newton's experiment, like them the arbors are subject to the same causes of attraction. Thus oil should stay at their meeting point, consequently at the pivots. Therefore if oil in conventional watches leaves the pivots and rises onto the pinions, this effect can only be produced by the convergence of their leaves, which attracts the fluid more strongly than the meeting points of the arbor and the plates; therefore, to maintain a sufficient amount of oil at this point and in the pivots, the pinions must be placed at a sufficient distance." Experiment confirmed this reasoning perfectly, for M. le Roy placed bearing plates in watches at the appropriate places to extend the oilers and the distance of pinions and wheels from the pivots; in cases where bearing plates could not be used, he substituted recesses and sinks and was pleased to see that the oil stayed on the pivots and in the cups without rising into the pinions or spreading as previously. See Plate (bearing), Sink, Noyon, etc.

It is extremely important that the balance should always be perfectly free, and that its pivots should bear on their tips and not on their tapers, therefore it was necessary in order to maintain oil in them to seek a new configuration of the parts. M. le Roy has found one that is most simple and advantageous.

To get an accurate idea of it, take a watch and put a drop of oil in the center of the crystal; then lay a transparent plane on it, a piece of glass for example, and the drop will be seen to arrange itself in a circle at the summit of the crystal. It will also be seen, when the glass is lifted, that the drop will shrink without letting go.

In order to produce the effect resulting from this experiment, M. le Roy adds to the cock in his watches three small, easily-made pieces: the lower one called the brass endpiece, See Cock (endpiece), acts like the crystal; the upper one, called the steel endstone, holds a small agate, as the hand holds the glass in the experiment, and since the tip of the balance staff rests on the center of the agate, it is always generously furnished with oil. At for the other pivot, a single part called an insert, See Inserts, is sufficient, since the potence functions as the other two. On this matter, one may consult a paper that M. le Roy has included at the end of La Règle artificielle du temps ; it concludes saying, "the better use horologists and mechanics in general can make of attraction and cohesion, in designing the parts of their mechanisms to hold oil at the necessary places, the closer they will come to perfection."