Page:Popular Science Monthly Volume 60.djvu/147

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nickel steel with its small coefficient of expansion appears to have a future for many purposes; can it by some modification be made still more useful to the engineer?

We owe much to the work of the Alloys Research Committee of the Institution of Mechanical Engineers. Their distinguished chairman takes the view that the work of that committee has only begun and that there is scope for research for a long time to come at the National Physical Laboratory, and the executive committee have accepted this view by naming as one of the first subjects to be investigated the connection between the magnetic quality and the physical, chemical and electrical properties of iron and its alloys with a view specially to the determination of the conditions for low hysteresis and non-aging properties.

At any rate we may trust that the condition of affairs mentioned by Mr. Hadfield in his evidence before Lord Rayleigh's commission which led a user of English steel to specify that before the steel could be accepted it must be stamped at the Reichsanstalt will no longer exist.

The subject of wind pressure again is one which has occupied the committee's attention to some extent.

The Board of Trade rules require for bridges and similar structures (1) that a maximum pressure of 56 pounds per square foot be provided for, (2) that the effective surface on which the wind acts should be assumed as from once to twice the area of the front surface according to the extent of the openings in the lattice girders, (3) that a factor of safety of 4 for the iron work and of 2 for the whole bridge overturning be assumed. These recommendations were not based on any special experiments. The question had been investigated in part by the late Sir Wm. Siemens.

During the construction of the Forth Bridge Sir B. Baker conducted a series of observations.

Table II.

Revolving Gauge
Mean Pressure.
Small Fixed Gauge.
Large Fixed Gauge.
W.W. W.W. W.W.
0 to 5 3 .09 3 .47 2 .92 2 .04 1 .9
5 to 10 7 .58 4 .8 7 .7 3 .54 4 .75
10 to 15 12 .4 6 .27 13 .2 4 .55 8 .26
15 to 20 17 .06 7 .4 17 .9 5 .5 12 .66
20 to 25 21 .0 12 .25 22 .75 8 .6 19
25 to 30 27 .0 28 .5 18 .25
30 to 35 32 .5 38 .5 21 .5
Above 65 41 .0 35 .25
(One observation only
above 32.5)

The results of the first two years' observations are shown in Table II. taken from a paper read at the British Association in 1884. Three