— 138 — 
Lidliüi.edto, the diameter of the pms will be almost eight- tenth« of the depth of tlie bars, 
and will be great enough to resist the bending- moments produced by any legitimate 
method of packing. Moreover, after the diameters of the pins have been deter- 
mined, the chord can be packed, if it be advisable, so as to reduce the bending- 
moments. This superabimtlance of strength in the pins is obtained at tlie expense 
of a slight increase in the weight of iron ; and the increased sizes of heads for diag- 
onals can do no harm, because they clo not enter any limited space, as do the heads 
at tlieir other ends. 
But if, by a skilful arrangement of the packing, we can so reduce the bending- 
moments on the pins, that the diameters may be made small, and the proportion of 
width to depth of bars larger tlian ihat ibiincl in tlie last chapter, the pins may not 
bo as strong as 、ve imagine them ; lor we cannot be sure that all the bars are going 
to pull as avc Lave asbiimed that they 'vili. It may be tliat one of the outer bars iii 
a trifle long, mid 、\ill not pnli at all until the others are well stretclied : what, theu, 
becomes of our calculated bencliiig-moments ? 
Any one of them may be ,mc> greatly exceeded, that the pin will be strained 
beyond the elastic limit, and will bend perceptibly, so clianging the distribution of 
stress in the panel that one or more of the bars also may be strained beyond the 
elastic limit. 
But if the pin be large enough, or more than large enough, it cannot bend per- 
ceptibly : consoqucntly the distribution of stress will be much more uniform, even 
it. the bars be of slightly uncciual lengths. 
