i04 Mr. Toivn^s new mode of ^ridge-huilding, 



which the mode itself does not command, even on the most 

 strict philosophical investigation as to its mathematical prin- 

 ciples, the easy, practicahle, and advantageous application 

 of materials, the advantages it possesses in mechanical ex- 

 ecution, and its simplicity, strength, economy, and durabili- 

 ty, as a general and uniform mode of Bridge-building. 



Science and practice will, in a short time, decide on this 

 question so important to this extensive country. 



I shall conclude this article by a few ideas, taken from 

 the .celebrated Robert Fulton's treatise on canal navigation, 

 page 117, and subsequent pages. 



In England, the attention of engineers has of late years 

 been much engaged on bridges of iron. These bridges, 

 as experience produces courage, are progressively enlarging 

 their dimensions, nor should I be surprised if genius should 

 in time, produce the mechanic rainbow of one thousand 

 feet over wide and rapid rivers. In crossing the rivers it> 

 such countries as Russia and America, an extensive arch 

 seems lo be a consideration of the first importance, as the 

 rivers or even rivulets, in time of rain, suddenly swell to a 

 great height, and in the spring, on breaking up of the ice, 

 the immense quantity which is borne down with a rapid 

 stream would, if interrupted by small arches and piers, col- 

 lect to such a weight as ultimately to bear away the whole. 

 It is therefore necessary tliat, in such situations, an arch 

 should be extended as far as possible, and so high as to 

 suffer every thing to pass through, or the inhabitants must, 

 v/ithout some other expedient, submit their passage to the 

 casualities of the weather. 



The important objeclion to bridges of wood is their 

 rapid decay, and this objection is certainly well founded 

 when particular situations are alluded to where timber is 

 scarce and consequently expensive. But in such countries 

 as America where wood is abundant, J conceive it will be a 

 fair criterion to judge of their application by calculating on 

 the expense of a bridge of stone, and one of wood, and 

 then compare the interest of the principal saved in adopt- 

 ing the wood bridge, with the expense of its annual repairs. 



I have before exhibited the necessity of constructing 

 bridges in America of an extensive span or arch, in order to 

 suffer the ice and collected waters to pass without interrup- 



