388 REPORT— 1892. 



enable the general laws to be determined. Thus we find Regnault, in 

 his classical experiments on the properties of steam, plots his results, as, 

 for instance, the ' saturation curve,' which was drawn in terms of pressure 

 and volume, on a copper plate. Almost all experimental work, such as 

 that of Ramsay and Young on ' Vapour Tensions,' contributed to tbe 

 Royal Society, Beauchamp Tower on ' Friction of Bearings,' Kennedy on 

 ' Engine Trials,' Thurston on ' Lubricants,' has been thus plotted; and 

 amongst numerous examples which might be quoted of the plotting of 

 results leading to the discovery of a law, we may quote the results of 

 tests on the strength of cement, which Professor Unwin has shown to 

 obey comparatively simple laws, the curves of test approximating to a 

 parabolic curve.' 



The following remark, taken from the preface of the important treatise 

 of Gangaillet and Kutter,^ well illustrates the advantages of this method : 

 ' In studying the subject we made continual use of the graphic method, 

 and were eventually led to the recognition of the elements affecting the 

 flow of water, and thus to the development of our general formula.' 



(2) It has become recently more and more the practice to plot the 

 results of laws, and experimental data, which would always have been 

 given a few years ago in the form of a table. Thus we find in Moles- 

 worth's ' Pocket-Book ' plotted results for safe loads on various spans of 

 girders (p. 125) and for moving loads (p. 162). In Professor Unwin's 

 book on machine design we find a graphic table of the proportions of 

 pipes (p. 16, Part II., 1890), and another on the proportions of keys 

 (p. 171, Part I., 1890), and in a more recent book by Foley ^ we have 

 the following examples of the graphical method : — Plotting of curves for 

 the expansion of steam for purposes of actual reference, the proportions 

 of valves, the extension and loading of springs, of friction, of the propoi"- 

 tion of the teeth of wheels, of proportions of belts, strengths of ropes, of 

 the displacements of ships, of the proportions of propellers, bolts, pipes, 

 boilers, furnaces, tubes, girders, coal consumption, surface condensation, 

 &c., all of these being on a large scale and elaborately prepared, so as to 

 enable actual proportions to be obtained by their use. 



Falling under the head of ' graphical tables ' are the constructions 

 devised by M. L. Lalanne,'* and published under the following title: — 

 ' Memoire sur la Table Graphique et sur la geometric anamorphique 

 appliquee a diverses questions qui se rattachent a I'art de I'ingenieur.' 

 An example of one of these tables, called by the inventor an ' abacus ' 

 (ahaque), was shown as a wall diagram to the Mechanical Section. The 

 ordinates and abscissae of this diagram are not numbered according to 

 their actual values, but are logarithmic, exactly as the scale on a slide 

 rule. By means of this diagram operations of multiplication can at once 

 be performed, and by a slight modification products such as a^b and the 

 \/ a^h can be readily obtained. 



Professor Culmann, in his book on graphic statics, gives another 

 table in which parabolic curves are plotted, by means of which a large 

 number of questions of earthwork cuttings and embankments can be 



' The Testing of Materials of Construction. Professor Unwin, B.Sc. Longmans, 

 Green & Co. 



^ A General Formula for the Uniform Flow of Water, by Ganguillet and W. R. 

 Kutter. Trans. Hering and Trautwine. Wiley, New York, 1889. 



' .Vfichanical Engineer's Reference-Booh. Foley. Crosby, Lockwood & Co., 1891. 



* AnnaUs des Fonts et Chaussees, 1846, tome i. 



