Proceedings of tee Polytechnic Association. 987 



plete specimen for an illustration of it ; still I hope a tolerabl}' clear 

 idea may be formed of the whole plan. 



In a structure, particularly in such as a bridge, there must bs no 

 guess work ; there must be harmony and Gonsistcncy of all the parts 

 throughout ; in a word, there must be a certainty as regards perfect 

 security under all circumstances. 



It is well known to all engineers, and to all persons of judgment, 

 that the security of a bridge depends either on rigidity or tensile 

 strength, or the two combined. 



It is also well known in mechanics, that the more simple the mode 

 of construction the better and the more reliable will be the strueture. 



In the plan I propose, all that is required to build a bridge is sim- 

 ply to bend tubes or rods to the pi'oper shape and size of the bridge, 

 and slide these tie blocks to their respective places ; and then pass 

 the longitudinal or connecting rods of soft steel (either in the shape 

 of rods or steel wire cables) through these holes in the tie blocks, and 

 cross ribs, in one piece (or its equivalent) ; and then secure well these 

 lono^itudinal soft steel rods or cables, throughout the whole ieno;th of 

 the bridge to the abutments ; thus doing away altogether with bolts, 

 nuts, tie rods and braces, and with any cutting of the parts whatever. 



And having symmetrically well combined and harmonized the 

 whole structure, the bridge will possess all the strength inherent in 

 the metal itself; combining in the same structure both the truss and 

 the suspension systems. Because, let it be well understood, the 

 component parts have not in the least been aifected by boring or 

 cutting away ; but on the contrary, each remains altogether whole 

 and a perfect unit, allowing expansion or contraction at divers tem- 

 peratures, with perfect freedom throughout; and without any undue 

 strain to one part of the structure, at the expense of another. 



As the main strength and security of all bridges depend principally 

 on tlie combined tension of the longitudinal connections ; and as 

 every one of these soft steel «onnecting rods, ov cables, is held firm 

 at the abutments independently of the others, according to my plans; 

 it follows, from the whole arrangement, that each rod or cable can 

 be tested at all times, and the strength of the structure as a whole, 

 can thus be always determined with positive certainty. 



Phenomena of Color. 

 Dr. P. II. Yanderweyde said it was Sir Isaac IN'ewton who first 

 started the investigation of color in a scientific manner. He discovered 



