Mr. Town’s new mode of Bridge-building. 168 
_ other mode, as by dividing the strain or stress into so ma- 
ny parts, that what falls upon any one part or joint is easily 
sustained by it without either the m ode of securing the 
10. The e expense of the superstructure of a bridge would 
not be more than from one-half to two-thirds of other 
modes of constructing one over the same span or opening ; 
this is a very important consideration, especially in’ the 
southern and nn States, where there are many wide 
rivers, and a — scattered population to defray the ex- 
penses of bridge 
11. This mode of securing the braces by so many trunnels, 
sth ey are in ee ein 
than could be had in the common “mode of se 
means of tennons and mortices, for tennon - shor 
and not very thick, compared with this aaa nor. havi 
so much hold of the pins or trunnels as in this case, will, of 
cere 
equal to, and in others greater than, the thrust or pushing 
strain. It is also very obvious, that thi is pushing or thrust 
ain in the mode of tennons and mortices receives very 
little additional strength from the shoulders of the tenons, 
as the shrinkage of the timber into which the tennon goes, is 
generally so much as to let the work settle so far as to give 
a motion or Serpe itn. which, in time, renders them scsi 
and insufficien 
"42: Should any kind of ister bridge, for any reason, 
be preferred, however it may be arched either at top or bot 
tom, or both, still this same mode of combining the mate- 
rials, will have all the advantages as to cheapness and 
strength, over the common ones of framing, as in case 
the horizontal or straight ones before described. - cases 
wee e abutments are already built, it sa. sometimes be 
ea Sidewalks cs nay wi _ a ease be constructed, either 
on the outside or inside of the main ody of the bridge, 
which anata paces the great strength of the mode, &c. 
may he better seen by examination ‘of the models which 
claimed in this new mode of c construction, by the patentee 
