THE ROYAL ARTILLERY INSTITUTION. 
845 
The shot in this figure is drawn as central: in point of fact, the face of 
the stud bears on the bottom of the groove: the windage under the body of 
the shot is 0*032, above it 0*066, which insures easy loading. General 
Didion, writing in February I860,* claims to have been the first to propose, 
as far back as 1850, to centre a rifle shot in the bore of a gun by the 
pressure of eccentric planes on the bearing surface of the studs. He 
observes, “ Further experiments were made at 
the School of Artillery la Fere in succeeding 
years, in which two buttons whose profile was 
not eccentric (this was the system adopted in 
1858) took the place of the single ailette . 
Those buttons presented certain inconveniences 
and at the present time (February 1860) they 
are making further trial on the system of 
eccentric ailettes we see the result in the 
above profile. The face of the stud it is true is 
still concentric, but the bevel of the driving 
edge, fulfils the part of its eccentric face Gen. Didion’s proposal of i860. 
(Fig. 2), and constitutes a part of the difference 
between the shells which failed in 1859 and those which succeeded in 1865. 
The bottom of the groove is struck from a centre about 0*31 of radius to the 
left of the centre of the bore. The breadth and depth are not stated, but 
have been enlarged to the scale of Fig. 1, shewing if they are truly pro¬ 
portioned in the original, a very much smaller stud than is now employed. 
There are three patterns of projectiles, viz. those of 1859, 1861 and 1863. 
The following details refer to the latter. The principal difference is in the 
size and profile of the studs;—but it must be understood that the different 
powers which have based their system of field artillery on that of the 
French, have by no means adhered closely to the form of projectile, see for 
example. Figs. 3 and 4 of the annexed Plate I., which are the common shells 
of the Swiss Federal and of the Wurtemburg artillery respectively. 
Table II. 
PRINCIPAL DETAILS OF THE COMMON SHELLS. 
mm. is. 
Diameter of shell (liigh gauge) .... 84*3 3*319 
do (low gauge) ... 83*7 3*296 
Higli gauge of studs or ailettes . 91*2 3*591 
Length of the cylindrical part .. 88*0 3*465 
Total length (minimum). 160*0 6*299 
Diameter of the zinc studs. 15*5 0*610 
Projection of the zinc studs . 3*6 0*142 
Interval between the two rows of studs, from 
centre to centre, sockets ( alveoles ) . 60*0 2*362 
Centre of the posterior row of studs from the 
bottom of the shell. 15*0 0*591 
Thickness of metal in the body of the shell . 12*85 0*506 
Thickness of the bottom of the shell . 12*75 0*502 
Diameter of fuze-hole to bottom of thread . 25*0 0*984 
Weight of shell empty . 3*66 kil. 8*08 lbs. 
Mean normal weight, charge, and fuze complete 4*07 n 8*97 u 
Weight of bursting charge. 0*2 n 0*44 n 
* Traite de Balistique, p. 425. 
