jyir. Toivn^s new mode of Bridge-building. 163 



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 witliout either the mode of securing the 

 joints, or the strength of the material being insuflicient. 



10. The 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 

 southei'n and western States, where there are many wide 

 rivers, and a very scattered population to defray the ex- 

 penses of bridges. 



1 1 . This mode of securing the braces by so many trunnels, 

 gives them much more strength when they are in tension-strain 

 than could be had in tlie common mode of securing them 

 hj means of lennons and mortices, for tennons being short, 

 and not very thick, compared with this mode, nor having 

 so much hold of the pins or trunnels as in this case, will, of 

 course, have much less power to sustain a tension or pulling 

 strain, and it is obvious that this strain is in many cases 

 ccpjal to, and in others greater than, the thrust or pushing 

 strain. It is also very obvious, that this pushing or thrust 

 strain in the mode of tennons and mortices receives very 

 little additional strength from the shoulders of the tennons, 

 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 vibration, which, in time, renders them weak 

 and insufficient. 



12. Should any kind of arched 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 of 

 the horizontal or straight ones before described. In cases 

 where abutments are already built, it may sometimes be 

 preferred. 



Side-walks may with equal ease be constructed, either 

 on the outside or inside of the main body of the bridge, 

 which particular, as also the grea.t strength of the mode, &;c. 

 may he better seen by examination of the models which 

 are (or soon will be) placed in most of the principal cities 

 of the United States, and no merit is either desired or 

 claimed in this new mode of construction, by the patentee, 



