may suppose about 10% of work is lost
by friction in the bore: this is expressed by saying that the _factor of
effect_ is f = 0.9.

The experimental determination of the time of burning under the influence
of the varying pressure and density, and the size of the grain, is thus of
great practical importance, as thereby it is possible to estimate close
limits to the maximum pressure that will be reached in the bore of a gun,
and to design the chamber so that the G.D. of the charge may be suitable
for the weight and acceleration of the shot. Empirical formulas based on
practical experience are employed for an approximation to the result.

A great change has come over interior ballistics in recent years, as the
old black gunpowder has been abandoned in artillery after holding the field
for six hundred years. It is replaced by modern explosives such as those
indicated on fig. 4, capable of giving off a very much larger volume of gas
at a greater temperature and pressure, more than threefold as seen on fig.
8, so that the charge may be reduced in proportion, and possessing the
military advantage of being nearly smokeless. (See EXPLOSIVES.)

The explosive cordite is adopted in the British service; it derives the
name from its appearance as cord in short lengths, the composition being
squeezed in a viscous state through the hole in a die, and the cordite is
designated in size by the number of hundredths of an inch in the diameter
of the hole. Thus the cordite, size 30, of the range table has been
squeezed through a hole 0.30 in. diameter.

The thermochemical properties of the constituents of an explosive will
assign an upper limit to the volume, temperature and pressure of the gas
produced by the combustion; but much experiment is required in addition.
Sir Andrew Noble has published some of his results in the _Phil. Trans._,
1905-1906 and following years.

AUTHORITIES.--Tartaglia, _Nova Scientia_ (1537); Galileo (1638); Robins,
_New Principles of Gunnery_ (1743); Euler (trans. by Hugh Brown), _The True
Principles of Gunnery_ (1777); Didion, Helie, Hugoniot, Vallier, Baills,
&c., _Balistique_ (French); Siacci, _Balistica_ (Italian); Mayevski,
Zabudski, _Balistique_ (Russian); La Llave, Ollero, Mata, &c., _Balistica_
(Spanish); Bashforth, _The Motion of Projectiles_ (1872); _The Bashforth
Chronograph_ (1890); Ingalls, _Exterior and Interior Ballistics, Handbook
of Problems in Direct and Indirect Fire_; Bruff, _Ordnance and Gu