1901.] on the Aims of the National Physical Laboratory. 663 



These slides are sufficient to call attention to the changes which 

 occur in solid iron, changes whose importance is now beginning to 

 be realised. On viewing them it is a natural question to ask how all 

 the other properties of iron related to its structure ; can we by special 

 treatment produce a steel more suited to the shipbuilder, the railway 

 engineer or the dynamo maker than any he now possesses? 



These marked effects are connected with variations in the condition 

 of the carbon in the iron ; can equally or possibly more marked 

 changes be produced by the introduction of some other element ? 

 Guillaume's nickel steel, with its small coefficient of expansion, ap- 

 pears to have a future for many purposes ; can it or some modification 

 be made still more useful to the engineer ? 



We owe much to the investigations of the Alloys Research 

 Committee of the Institution of Mechanical Engineers. Their dis- 

 tinguished chairman holds the view that the work of that committee 

 has only begun, and that there is scope for such research for a long 

 time to come at the National Physical Laboratory. 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 especially to the determination of the 

 conditions for low hysteresis and non-agency 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 Eeichsanstalt, will no 

 longer exist. 



The subject of wind pressure, again, is one which has occupied 

 this committee's attention to some extent. The Board of Trade 

 rules require that in bridges and similar structures (1) a maximum 

 pressure of 56 lbs. 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 W. Siemens. 



During the construction of the Forth Bridge Sir B. Baker con- 

 ducted a series of observations. 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 gauges were used. 



In No. 1 the surface on which the wind acted was about 1^ square 

 feet in area ; it was swivelled so as always to be at right angles to the 

 wind. In No. 2 the area of surface acted on was of the same size, but 

 it was fixed with its plane north and south. No. 3 was also fixed in 

 the same direction, but it had 200 times the area, its surface being 

 300 square feet. 



