1887.] NEW YORK ACADEMY OF SCIENCES. '153 



the principle of the arch and the suspension principle ever at- 

 tempted ; and that it is, altliough constructed entirely of timber, 

 without a nail or a spike except those used in the board covering, 

 the prototype of nearly all modern constructions in iron which 

 have of late years become so numerous, and which are classified 

 as braced girders. This bridge was devised and erected by Ithiel 

 Towne, about the year 1823, for the New Haven and Hartford 

 Turnpike Company, across the Mill Eiver. It is 100 feet long, 

 fourteen feet wide, and twelve feet high, and is built on the 

 principle of straight top and bottom chords, connected by diago- 

 nal bracing ; a principle invented by Mr. Towne and never be- 

 fore introduced into bridge construction. 



About the year 1840, Mr. Eli Whitney, of New Haven, who 

 was then constructing the dam and reservoir on Mill River, 

 which now supplies New Haven with water, removed tliis bridge 

 bodily on skids from the point where it was first erected to the 

 place it .now occupies, about half a mile distant — a difficult feat 

 of engineering, but accomplished without removing or displacing 

 a single timber of the bridge. The bridge is thus probably the 

 oldest timber bridge of any considerable span in this or any 

 other country, having fortunately escaped the fate of nearly all 

 large timber bridges — destruction by fire. 



The principal parts have never been renewed, and, thanks to 

 the board covering, these parts are still sound and serviceable. 



I have dwelt at some length on the history of this particular 

 bridge, because the interesting feature of its construction 

 was the employment of an entirely new principle in bridge con- 

 struction which, by mere change from timber to wrought iron 

 and steel, has been followed ever since. Details have changed, 

 the modifications giving rise to various types as they are known 

 at the present day, but the fundamental principle has been 

 almost universally adopted in all countries, and remains un- 

 altered. 



The tubular bridge, a later design, of which the famous Menai 

 Bridge, erected by Stevenson and Fairbain across the Menai 

 Straits, is the most conspicuous example, has had no important 

 development, skeleton structures being now universally pre- 

 ferred. 



