SUSPENSION BRIDGES.

Evening Star, Volume VIII, Issue 2216, 14 June 1870, Page 2

SUSPENSION BRIDGES.

To the Editor of the Evening Star. Sir,—Your leader of yesterday is devoted to a topic which appears to create some little interest in the engineering circle—whether from the novelty of the construction referred to, or the fact of an engineering genius (as Mr Poyman is made to appear) being so long in .Otago without giving the public the benefit of his skill, I know not; but to judge from that gentlemen’s reply to my letter on the subject, I would certainly not suppose him to be one of the high lights of the engineering profession You say, Mr Editor, Mr Poyman's bridge is not a suspension. Now, I ask, why docs Mr Peymau apply for a patent for a wire suspension bridge ? Gas it really, sir, been left to you to discover for him that it is not what he represented ? I was rather startled at that discovery, for 1 contend it is a suspension bridge, and moreover a facsimile of one erected by me more than three years .ago, and I must say mine is called a suspension bridge. I f this bridge is not supported from above, but takes its bearings or props itself against the abutments, then it is certainly not a suspension, but a common arched bridge, and the wire ropes, I presume, are there only for ornament. But 1 find you want to show tho wire ropes are necessary to hold it up ; so what will we call it‘i -the. patent hermaphrodite bridge. You must pardon me, Mr Editor, for presuming to differ from you, but this is a subject of public importance, and should be well ventilated, or 1 might say kept no longer iu suspension. You say the roadway is laid upon two lower lines transversely, and abutting upon the masonry at each end of tho bridge, and connected to the top ropes by rigid iron rods. Now I want to know are the rigid iron rods to keep up the top ropes, or the top ropes to keep them up, and they in turn to keep the bridgel confess you have puzzled me on that point, for your explanation has utterly failed in explaining to me as to whether it is a suspension or a common arched bridge. In the name of common sense, Mr Editor, how could rigid iron rods connected to suspension ropes prevent any undulation in the roadway, when it itself is laid up m wire ropes ? Does it not strike you that the shrinking or swelling of the planking of such a roadway ’endangers the safety of the construction if you depended upon the. arched roadway, which you say iu itself wouldjbear an enormous weight '!

In conclusion, I wish to say that I am not condemning the principle of the bridge, but I differ with you as to where the strength of the bridge lies, and also to Mr Poyman taking credit. as being the inventor, when 1 have shown that I erected one upon the same principle, and take less credit to myself for the idea than for the actually carrying it out. Trusting some professional man will think it worth his while to settle the matter, and not leave it exclusively to myself, Yours, &c., Wm. Frr.r.KK. Kerosene Bond, .Time 10.