698 
MR. FAIRBAIRN’S EXPERIMENTAL INQUIRY 
possible, it will be neeessary to consider it in this paper with others of equal import- 
ance and probably of more general use. 
The system of countersinking the rivets is only used when smooth surfaces are re- 
quired ; under other circumstances their introduction would not be desirable, as they 
do not add to the strength of the joint, but to a certain extent reduce it. This re- 
duction is not observable in the experiments, but the simple fact of sinking the head 
of the rivet into the plate and cutting out a greater portion of metal, must of necessity 
lessen its strength, and render it weaker than the plain joint with raised heads. This 
must appear evident from the fact of the sectional area of the plate being diminished, 
and the consequent reduction of the heads of the rivets, which in this state are less 
able to sustain the effects of an oblique or transverse strain. 
It is, however, satisfactory to observe that countersinking the heads of the rivets 
does not seriously injure the joint in its powers of resistance to a direct tensile force; 
but the rivets are liable to start when exposed to collisions or a strong impinging 
force, such as the sides of ships are frequently doomed to encounter. 
On referring to experiments (Table XL), the same results as to strength are ob- 
tained with the countersunk rivets as those with rounded heads ; they are rather 
under the mean of the former experiments, but not more than is easily accounted for 
by the reduced section of the countersunk plates. 
The joint with plates, riveted on each side, is seldom used, a circumstance which 
probably arises from its greater complexity of form and the danger which a treble 
thickness of plate would be subject to if used in boilers or vessels exposed to the ac- 
tion of intense heat. It is also inadmissible in ship-building, as the smooth surface 
requires to be maintained, and the greatest care observed in the formation of the outer 
sheathing to lessen the resistance of every part of the hull immersed in the water. In 
other respects the double-riveted plate is a strong joint, and in every case, where 
great strength is required, it may be used with perfect safety. 
It will be unnecessary to go through a further comparison of the experiments, as 
sufficient data have already been furnished to enable us to calculate the force per 
square inch, and to resolve the whole into a general summary exhibiting the relative 
strengths — 1st, of the plates; 2ndly, of the single- and double-riveted joints; and 
lastly, the ratio of the strengths as deduced from the whole series of experiments. 
