ons which surround our balance are very constant, the small
pivots turning in fine hard jewels lubricated with an oil on which
exposure to the action of the air has little effect, leaves but few
influences which can interfere with the regular action of our balance.
We add to the influences an adjustable correction for the disturbances
of heat and cold, and we are convinced that but little could be added.

ANTAGONISTIC INFLUENCES.

In this combination we have pitted two antagonistic forces against each
other, viz., the elasticity of the spring and the weight and inertia of
the balance; both forces are theoretically constant and should produce
constant results. The mechanical part of the problem is simply to afford
these two forces perfect facilities to act on each other and compel each
to realize its full effect. We must also devise mechanical means to
record the duration of each conflict, that is, the time length of each
vibration. Many years have been spent in experimenting to arrive at the
best propositions to employ for the several parts to obtain the best
practical results. Consequently, in designing a chronometer escapement
we must not only draw the parts to a certain form, but consider the
quality and weight of material to employ.

To illustrate what we have just said, suppose, in drawing an escape
wheel, we must not only delineate the proper angle for the acting face
of the tooth, but must also take cognizance of the thickness of the
tooth. By thickness we mean the measurement of extent of the tooth in
the direction of the axis of the escape wheel. An escape-wheel tooth
might be of the best form to act in conveying power to the balance and
yet by being too thin soon wear or produce excessive friction. How thick
an escape wheel should be to produce best results, is one of the many
matters settled only by actual workshop experience.

FACTORS THAT MUST BE CONSIDERED.

Even this experience is in every instance modified by other influences.
To illustrate: Let us suppose in the ordinary to-day marine chronometer
the escape-wheel teeth exerted a given average force, which we set down
as so many grains. Now, if we should employ other material than
hammer-hardened brass for an escape wheel it would modify the thickness;
also, if we should decrease the motive power and increase the arc of
impulse. Or, if we should diminish the extent of the impulse arc and add
to the motive force, every change would have a controll