1829.] 
355 
Into the Hmmalaya Mountains . 
be carried without any difficulty on the worst roads. A coil of 4^ or 5 * inch rope, 
the weight of which would be probably five or six cwt. is not so easily disposed of. 
In point of durability, including attention and repairs, the advantage is equally 
great ; a chain bridge once properly erected, requires little or no care, and the ex- 
pense is confined to an annual cost of paint, or coal tar; either of which, will effectually 
preserve iron for many years, however inclement the weather to which it may be 
exposed. The rope -bridges which were erected in Kam&fiu, on the contrary, 
required constant attention, and the maintenance of an extensive establishment, as 
well for tightening the ropes, as to preserve them from intentional mutilation. Dur- 
ing eight months of the year, they were wholly removed and lodged in storerooms. 
Yet with all these precautions they are not expected to last in the hills above two 
seasons. In convenience, therefore, as well as in actual safety, iron must be always 
superior to rope, which from its flexibility, however well secured or supported by 
guys, is ill adapted for bridges. This is so obvious that it is unnecessary to insist 
more on it. 
Thus we see that in economy, whether as regards prime cost, expence of carriage, 
expence of management, or durability, iron has a great and manifest advantage over 
rope as a material for bridges. In point of convenience, whether as regards faci- 
lity of carriage, durability, or as requiring little attention, it is also greatly superior. 
The erection of bridges every year, and their reconstruction every two years, 
would be a seriously inconvenient arrangement, even were it not an expensive one. 
Lastly, there can be little doubt of its being the most safe material, in as much as it 
is, strength for strength, only half the weight; being scarcely subject to deteriora- 
tion from exposure, it is not liable suddenly to become insecure in consequence of 
any unusual or unseasonable weather, or casual inferiority of material ; and lastly, 
not being subject to the stretching and tightening of rope, it is not liable to suffer 
from any change in the figure of the bridge, or alteration of strain on the parts. 
The above points have been so clearly established, and are now so generally 
admitted, that there is every prospect of this bridge being extensively introduced 
within the hills ; and doubtless, it is one of the greatest boons the mountaineers 
have yet received from their European masters. Tables have been furnished, by 
which any engineer or executive officer may at once determine the expense of tltefee 
bridges, according to their span and the weight they are required to carry. The 
following are the particulars of three different sizes which may, we think, be inte- 
resting to many. 
Dim. of bridge. 
Section of iron 
for chains. 
Probable 
weight of fi- 
nished iron 
work. 
Prob. Exp. of 
j iron work 
| deliverable 
1 at the H. C. 
1 yard. 
Estimat- 
ed weight 
of plat- 
form. 
Equiva 
lent to 
men. 
Length. 
Breadth. 
20 lbs. 
pr. square 
foot. 
■ ft- 
ft- 
Sq. inch. 
Fy. mds. 
Sa. Rs. 
lbs. 
lbs. 
100 
6 
2 
30 to 35 
360 
5,000 
12,000 
80 
150 
6 
3 
40 to 50 
480 
7,500 
18,000 
120 
200 
6 
4 
60 to 70 
720 
10,000 
24,000 
160 
Note 1. For retired and less frequented situations, lighter bridges might be 
constructed at, probable, one quarter the above expense ; the loads allowed for these 
being ample, and such as are not likely to be placed on any but military bridges. 
Note 2. In order to facilitate the carriage of the iron, the bars can be made of 
any length considered most convenient, so as to admit of the whole being earned by 
hill porters if necessary ; multiplying the numbers of joints must ot course increase 
the expense in some measure ; the above estimate supposes the bars not less than 
10 ft. in length. Such a bar having a sectional area of one inch, would weigh 27 to 
3° lbs. , . . , . 
Note 3. In calculating the comparative expense of iron, with that of any other 
material, the former may be assumed to last 20 years, at the expiration of which 
time, it might still be available for bridges of smaller span, or would at least be 
valuable and sell as old iron to be wrought up again. Its durability, however, will 
greatly depend upon its being occasionally cleaned and fresh painted or tarred. 
It will be useful to mark also the several modifications of form of which the 
iron-bridge is susceptible. The most obvious and secure against vibratory motion, 
as well as the most economical, is that represented in the accompanying elevation 
fig. 1. next page. The chains are carried straight across. 
