l,
the back-slope is formed next to the shoulder, although many persons seem
to think that this back-slope is merely added by way of ornament, to make
the pivot more graceful in appearance. It is very essential, however, for
if too much oil is applied the staff would certainly draw it away if its
thickness were not reduced, by means of the back-slope. Before leaving
the subject of capillarity let us examine the enlarged jewel in Fig. 5;
_c_ is an enlarged pivot, _b_ is the hole jewel and _a_ is the end stone.
We observe that the hole jewel on the side towards the end stone is
convex. It is so made that through capillarity the oil is retained at
the end of the pivot where it is most wanted. It is, in my opinion, very
necessary that the young watchmaker should have at least a fair
understanding of capillarity, and should understand why the end stone is
made convex and the pivot with a back slope. For this reason I will try
and make clear this point before proceeding further. We all know that it
is essential to apply oil to all surfaces coming in contact, in order to
reduce the friction as much as possible, and if the application of oil is
necessary to any part of the mechanism of a watch, that part is the
pivot. Saunier very aptly puts it thus: "A liquid is subject to the
action of three forces: gravity, adhesion (the mutual attraction between
the liquid and the substance of the vessel containing it), and cohesion
(the attractive force existing among the molecules of the liquid and
opposing the subdivision of the mass.)"

We all know that if we place a small drop of oil upon a piece of flat
glass or steel and then invert the same the oil will cling to the glass,
owing to the adhesion of the particles; if we then add a little more to
the drop and again invert, it will still cling, although the drop may be
elongated to a certain degree. This is owing to the cohesion of the
molecules of the oil, which refuse to be separated from one another. If,
however, we again add to the drop of oil and invert the plate the drop
will elongate and finally part, one portion dropping while the other
portion clings to the main body of the liquid. The fall of the drop is
occasioned by gravity overcoming the cohesion of the molecules. Now take
a perfectly clean and polished needle and place a drop of oil upon its
point and we will see that the oil very rapidly ascends towards the
thicker portion of the needle. Now if we heat and hammer out the p