THE ROYAL ARTILLERY INSTITUTION. 
81 
thickness of which has been exactly calculated with reference to the degree 
of sensitiveness required. (Fig. 4!,/*). 
The junction of the two cups round the horizontal circumference of the 
ball * 1 is covered with a strip of tissue paper varnished on and afterwards the 
ball receives the usual coverings of gut, silk, and varnish. 
2nd. The interior of the fuze is enlarged about the centre so as to make 
the blow which the ball strikes on impact equal in all directions. 2 (Fig. 4, a). 
PettmaiFs sea service fuze differs from the land service in a few other 
details of construction : it has no bottom plug, the bottom of the fuze being 
solid, with the exception of a small fire hole in the centre which is closed 
with a disc of cardboard, over which is varnished a disc of fine paper. 
The cone plug (Fig. 4, e ), is of an improved construction, the stud being 
prolonged downwards in the form of a hollow cylinder, which is driven and 
pierced like a tube, the lower end being closed with a cardboard disc. 3 This 
construction, and the absence of a bottom plug stud, necessitate a different 
arrangement for checking re-action: the lower part of the interior of the 
fuze is hollowed out or undercut, and the lead cup crushing outwards into 
this groove is securely held and the upper part of it having contracted round 
the stud of the cone plug, re-action is prevented. 
Externally the sea service fuze differs in being larger and screwed to fit 
the fuze holes of the naval or “ Moorsom ” gauge. 4 
The thread instead of being carried down the whole length of the fuze, 
only extends f " below the shoulder. 
The wrench holes in the sea service fuze are further apart than in the land 
service fuze, being adapted to the naval wrench. 
In other respects the PettmaiFs sea and land service fuzes are the same. 
The sea service fuze is also similarly marked with the number of thousand, 
numeral I., and month and year of issue, and lacquered. 
The action of the two fuzes is the same, with the exception that in the sea 
service fuze on the crushing of the lead cup, the tube of the cone plug is 
shot forth beyond the bottom of the fuze, forcing out the cardboard disc by 
each. It is evident that any increase in thickness will tend to render the fuze less liable to act on 
striking a ship’s side, while any decrease in thickness will tend to make it more liable to explode on 
striking water, and as the limits are very restricted, great delicacy and exactness is necessary in the 
manufacture of these cups. 
1 In some early experiments the junction was placed round the vertical circumference, hut pre¬ 
mature explosions resulted. This was believed to proceed from the partial separation of the cups 
on the shock of discharge and the scraping downwards of the cups over the detonating composition. 
The ball of the S.S. fuze is the same size as that of the L.S. fuze, but the position of the groove is 
not exactly round its circumference, as such an arrangement would bring the groove at the junction 
of the cups. The covered S.S. ball weighs more than the L.S. ball, owing to the copper cups, the 
limits are from 160 to 148 grains. 
2 This is an important point where the sensitiveness of the fuze has to be carefully regulated, since, 
evidently, however accurately that sensitiveness might be regulated for the fall of the ball with the 
fuze end on, if that fall were not exactly the same when the fuze struck sideways, the sensitiveness 
would be proportionally affected under such conditions of striking. In the L.S. fuze where the 
exact degree of sensitiveness is not considered, such an arrangement is of course unnecessary. 
8 This disc serves the purpose of the quickmatch in the L.S. fuze after the gun is fired, viz. 
prevents the powder dust from working into the fuze. 
4 The thread is therefore right-handed, 16| to the inch and of the “Moorsom gauge,” or, the 
same as that of the and 20 seconds time fuzes, and the old Moorsom fuze. 
