418 
MINUTES OE PROCEEDINGS QE 
considered independent of tlie pressure; and it is probable that when tbe 
rubbing surfaces of both projectile and groove (or other driving-surface) 
are of the same hard material, the coefficient of friction may be occasionally 
enormously increased. 
The resistance due to this cause might, under certain circumstances, be 
sufficient to ensure the destruction of the gun; and this view is to some 
extent corroborated by the occasional bursting of guns, the failure of which 
it is difficult to attribute to any other cause; and in the instances referred 
to, the recovered fragments of the shot were thought to exhibit decided 
appearances of seizure. 
If in equation (26) we substitute 8 for -, we shall have 
R 
G : 
2tt P 2 
Ml 
(2 Trp^lc — tJi) + 
V + (sin 8) 2 
(27 r P 2 sin 8 + rhjc) 
-(31) 
Eig. 4. 
And this equation will represent the ratio of the pressures R and G in any 
system of rifling, 8 being the angle which the radius makes with the normal 
to the driving-surface. Thus in an elliptically-bored 
gun (see fig. 4), the angle ORQ represents the angle 8, 
R 
and we obtain — by substituting in (31) the value of 
G 
this angle; by putting 8=90°, we may derive equation 
(13) directly from (31). 
We have not in this note entered into the question of 
the absolute pressures existing in the bores of ordnance 
of various natures, as the subject is too extensive and of 
too great importance to be disposed of within the limits 
of a short paper. 
Artillerists acquainted with the subject will be able to 
form rough approximations to these pressures from the J 
experiments made abroad with smootli-bored guns, with 
a view to the elucidation of this important question. It is much to be 
regretted that no experiments of the nature referred to have been attempted 
in England under Government auspices, as they are of a description which 
precludes their being satisfactorily made by private individuals, and as the 
information to be derived from them would be especially important in the 
case of rifled cannon, where so many new conditions are introduced into the 
problem as to render previous investigations of but little value. 
We shall, however, in a future note endeavour to discuss this subject, 
making use of the data at present at our disposal. 
