2g2 



NA TURE 



[July i8, 1901 



depression and at the same time other satisfactory properties. 

 The now well-known glass i6"' is the result. Its composition 

 is shown in the Table. 



The fact that there was an appreciable ditiference between the 

 scale of the 16" glass and that of the air thermometer led to 

 further investigations, and another glass, a borosilicate contain- 

 ing 12 per cent, of boron, was the consequence. This glass has 

 a still smaller depression. 



Previous to 1 888 Germany imported optical glass. At that 

 date nearly all the glass required was of home manufacture. 

 Very shortly afterwards an export trade in raw glass began, 

 which in 1S98 was worth 30,000/. per annum, while the value 

 of optical instruments, such as telescopes, field-glasses and the 

 like, exported that year was 250,000/. Such are the results of 

 the application of science, i.e. organised common sense, to a 

 great industry. The National Physical Laboratory aims at 

 doing the like for England. 



I have thus noted very briefly some of the ways in which 

 science has become identified with trade in Germany, and have 

 indicated some of the investigations by which the staff of the 

 Keichsanstalt and others have advanced manufactures and 

 commerce. 



Let us turn now to the other side, to some of the problems 

 which remain unsolved, to the work which our Laboratory is to 

 do and by doing which it will realise the aims of its founders. 



The microscopic examination of metals was begun by Sorby in 

 1864. Since that dale many distinguished experimenters, 

 Andrews, Arnold, Evving, Martens, Osmond, Koberts-Austen, 

 Stead and others, have added much to our knowledge. I am 

 indebted to Sir \V. Roberts-Austen for the slides which I am 

 about to show you to illustrate some of the points arrived at. 

 Prof. Ewing a year ago laid before the Royal Institution the 

 results of the experiments of Mr. Rosenhain and himself. 



This microscopic work has revealed to us the fact that steel 

 must be regarded as a crystallised igneous rock. Moreover, it 

 is capable, at temperatures far below its melting point, of .altering 

 its structure completely, and its mechanical and magnetic 

 properties are intimately related to its structure. The chemical 

 constitution of the steel may be unaltered, the amounts of 

 carbon, silicon, manganese, cic. , in the different forms remain 

 the same, but the structure changes, and with it the properties 

 of the steel. 



Sections of the same steel polished and etched after various 

 treatments show striking differences. For instance, if a highly 

 carburised form containing I '5 per cent, of carbon be cooled 

 down from the liquid state, the temperature being read by 

 the deflection of a galvanometer needle in circuit with a 

 thermopile, the galvanometer .shows a slowly falling tempera- 

 ture till we reach 1380° C, when solidification takes place; 

 the changes which "now ' go on take jilace in solid metal. 

 After a time the temjjerature again falls until we reach 6S0', 

 when there is an evolution of heat ; had the steel been free 

 from carbon there would have been evolution of heat at 895° 

 and again at 766°. Now throughout the cooling, molecular 

 changes are going on in the steel. By quenching the steel 

 suddenly at any given temperature we can check the change and 

 examine microscopically the structure of the steel at the tem- 

 peratu re at which it was checked. 



[Slides were shown representing the microscopic structures of 

 steels subjected to different treatment as regards temperature 

 and annealing.] 



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 thjin any he now possesses ? 



These marked eflects 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 ? (iuillaume's nickel steel, with its small coeffi- 

 cient of expansion, appears 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 

 distinguished chairman holds the view that the work of that com- 

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

 for along time to corneal 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 specially 

 to the determination of the conditions for low hysteresis and 

 non -agency properties. 



At any rate we may trust that the condition of afi'airs mentioned 

 by Mr. Hadfield in his evidence before Lord Rayleigh's Com- 

 mission 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 occu- 

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

 Trade rules require that in bridges and similar structures (i) That 

 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 tlie late Sir \V. Siemens. 



During the construction of the Forth Bridge Sir B. Baker 

 conducted 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. 



Table II. 



In No. I the surface on which the wind acted was about 

 li 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. 



In preparing the table the mean of all the readings of the 

 revolving gauge between o and 5, 5 and 10, &c., lbs. per square 

 foot have been taken, and the mean of the corresponding read- 

 ings of the small fixed gauge and the large fixed gauge set oppo- 

 site, these being arranged for easterly and westerly winds. 



Two points are to be noticed : ( i ) only one reading of more 

 than 32'5 lbs. was registered, and this, it is practically certain, 

 was due to faulty action in the gauge. 



Sir B. Baker has kindly shown me some further records with 

 a small gauge. 



According to these pressures of more than 50 lbs. have been 

 registered on three occasions since 1SS6. On two other occasions 

 the pressures, as registered, reached from 40 to 50 lbs. per square 

 foot. But the table, it will be seen, enables us to compare the 

 pressure on a small area with the average pressure on a large 

 area, and it is clear that in all cases the pressure per square 

 foot as given by the large area is much less tlian that deduced 

 from the simultaneoOs observations on the small area. 



The large gauge became unsafe in 1S96 and was removed ; 

 but the observations for the previous ten years entirely confirm 

 this result, the importance of which is obvious. The same 

 result may be deduced from the Tower Bridge observations. 

 Power is required to raise the great bascules, and the power 

 needed depends on the direction of the wind. From obser- 

 vations on the power some estimate of the average wind pressure 

 on the surface may be obtained, and this is foun<l to be less 

 than the pressure registered by the small wind gauges. Nor is 



NO. 



1655, VOL. 64] 



