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Page:Popular Science Monthly Volume 89.djvu/43

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�If a cable should snap, the crib would be dashed to pieces on the rocks below the falls

��THE work of lui i 1(1 ing cctTcr-danis, or t e m p o r a r y dams, is often as ticklish and difficult as the larger and sup- posedly more important fin- ished pivcc of construction which is impos- sible without the dams as a foundation.

The picture illustrates the

placing of a section of the crib-work of a coffer-dam. Observe that the water is in almost flood state, because the natural channel of the river has been so much restricted by the already com- pleted part of the work.

The cribs are built on dry land to verj^ accurate measurements. When all is ready, each one is laimched in its order. The methods of control, after launching, vary. In this case five steel wire cables of ^s-'i. diameter rigidly connected with five winches, located at points on the river banks, were used to control the course of the cribs as they were placed. When a new section is brought in line with the already existing

��Popular Science Monthly A Ticklish Moment

���To ascertain the time, simply pull the

watch down out of its case. The spring

will withdraw it when released

��29

work, it is held fast there by the cables and winches until the rock, piled at the end of the older part of the dam, is thrown into the spaces in the crib and the new section is thus "weigh- ted into place." Then thecables and all other lashings are removed and the ne.xt section treated in like manner. Something of the extent of the forces that have to be met with, due to the im- mense water pressure, may be gathered from the fact that during the placing of one of these cribs, one cable parted and the strain thus thrown upon the remaining four proved successively too much and they each in turn gave way. The crib meantime sailed gaily down stream, o\er the rocks and bumps of the falls below.

Where coffer-dams arc thrown across deep channels of treacherous waters the work is fraught with the greatest danger, necessitating the most careful system of operations.

A Protecting Holder for an Open-Faced Watch

WE illustrate an original idea in a watch-holder for wearing upon the person, especially for ladies' use, in which the watch is invisible and is jHilled down by a suitable pendant so as to allow the face to be seen. The illustration shows the holder as seen from the back, with the watch partly drawn down and out of the holder against the top spring. A crescent- shajjed piece receives the watch when drawn up. The watch may be of special shaped as here shown, or a flat disk can be used to serve as a watch-carrier, with an ordinary watch fitted into it by clamps. In this case the disk works with the spring and the pendant, allow- ing any watch of proper size to be fitted into it and carried with safety.

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