1829.] 
Into the Himnutlaya Mountains. 
353 
chains may be with great precision adjusted to any required strain, and no more : 
while in insistent bridges, the liability of the arch to a fatal derangement of its form 
from partial or excessive pressure, requires an enormous increase of weight, and of 
strength beyond what is requisite for the mere support of its load, supposing it were 
uniformly distributed. 
“ Iron, independently of its cheapness and extensive diffusion, is singularly and 
admirably adapted forthe construction of suspension bridges. When it is considered 
that the greater part of the weight of these bridges arises from the chains them- 
selves, it is evident, that the best, material for this purpose is that which has great 
tenacity with small weight, and thus we find that iron is at the same time the most 
tenacious, and excepting tin, the lightest of the common metals. A square inch of 
good iron requires about 28 tons to separate it, and it will not be stretched or other- 
wise affected with less than half that weight-” Mr. Ainger goes on to say, “ Where, 
however, economy and portability are important objects, rope bridges will be found 
advantageous, and they have been during the last few years extensively introduced 
into British India by Mr. Shakespear, the Post Master General at Calcutta. They 
have produced great benefit in facilitating the transport of troops and baggage, 
as well as of merchandise and the mails. One of these bridges, 160 ft. in length, 
is so lis'/it and portable , that it has been sevoal times set up and removed in a few 
hours." The reader will presently see, that, in giving this opinion, Mr. Ainger was 
not acquainted with the real value of the Shakespearian bridge. 
The merit, I believe, of first pointing out clearly the great superiority of the iron 
chain bridge over any that had yet been constructed of wood or rope, belongs to 
the present superintendent of that department. In 1828, nine bridges were sent 
up for the military roads about Almdrah, before mentioned. The span was from 
80 to 190ft. and the cost only 5,256 Its. being an average of 084 Rs. for each 
bridge. Sundry spare articles, amounting in the whole to 707 Rs- increased the 
above average 78 Rs. making it 626. One of these bridges alone, the 190 ft. span, 
cost Government, when constructed of wood, 10,000 Rs. and what is still more to 
the purpose, it was, in less than three years, condemned by a committee as unser- 
viceable. Their opinion was justified by the result ; for the following year, two un- 
fortunate men, having ventured to cross in spite of the repeated public notices that 
had been given, the bridge gave way, and they were lost. I believe the smallest of 
those bridges, as made of wood, did not cost less than 3000 Rs. and probably on an 
average, one with another, they cost 5000, or eight times the price of the iron chain 
bridges, which will probably last five times as long. The Shakespearian bridge waa 
found to have in economy, only the advantage of 5 to 8 ; so that the iron-chain 
bridges will be five times cheaper than these, contrary to Mr. Ainger’s and the 
inventor’s opinions. On this subject Ipropose to enter into a little detail. 
The strength of iron has been found, by experiment, to be nearly seven times 
greater than that of the freshest hemp rope (of European manufacture) . The weight 
then of two bridges of equal strength of iron and hemp, should be nearly equal, 
i. e. while dry. In practice, however, it is found that so many additional pieces are 
required in a rope bridge, as ties, slings, braces, &c, as to raise the weight of the 
rope bridge to double that of the iron, strength for strength. This in itself is a 
serious objection, independent of its reference to economy. The price of wrought 
iron is found to be from 10 to 12 Rs. per factory maund; that of good European 
hempen rope is 21 Rs. per cwt. or 56 seers, equal to about 16 Rs. per maund. \V'e 
see therefore, that even on the supposition of equal weights, rope is dearer by one- 
third than iron : if we take double the weight of rope, as shown above to be neces- 
sary, a bridge of rope will be nearly three times the cost of one of iron. 
Now, supposing a rope-bridge will last four years, (and this I think is a favour- 
able supposition,} an iron one will last ten 1 * ; and as it costs only a little more than 
one-third, the price is evidently more economical in the ratio of nearly six 
to one. It may however he said, that Europe hemp is dear, and that a cheaper 
material is on the spot (the Mulzun rope}, the adoption ot which, would make a 
great difference in this estimate. I shall therefore, as the best answer to this objec- 
tion, and as a means of showing the great superiority of iron, here compare tsvo 
estimates, the one showing the expense of a bridge of 165 ft, span to be constructed 
of rope, manufactured in the hills ; the other of an iron-chain bridge of the same 
span. That the latter estimate is not too favourable, will appear by the details I shall 
presently bring forward of what has been actually done. 
* The duration of an iron bridge is assumed as above, to allow of every advan- 
tage to the rope-bridge in the comparison ; but I believe, I might safely have said 
20 instead of 10. 
