September 19, 1895] 



NATURE 



50- 



Electrical engineering is very intimately connected with 

 physics, for it really is the application of electricity to industrial 

 inirposos. The very close relation between electricity and 

 magnetism, discovered liy (Jersted in 1820, an<l further estab- 

 lished by the remarkable researches of Earaday, has led to the 

 present system of generating electricity by the relative move- 

 ment of coiled conductors and electro-magnets, in dynamo- 

 electric machines worked by a steam-engine or other motive 

 power. The electrical current thus generated can be transmitted 

 to a distance with litile loss of energy ; and it can either be use<i 

 directly for lighting by arc or incandescent lamps, or be recon- 

 verted into mechanical power by the intervention of another 

 dynamo. Electricity is also employed for the simultaneous 

 firing of a series of mines, at a safe distance from the site of the 

 explosion. 



The convertibility of heat and energy, indicated by Mayer, 

 forms the basis of thermodynamics ; and the mechanical 

 equivalent of heat, a physical problem of the highest interest, 

 determined by Joule in 1S43, furnishes a measure of the amount 

 of work that can be possibly obtained by a given expenditure of 

 heat in heat-engines. 



The above summary indicates how the discoveries of physics 

 are ajiplied to many branches of engineering ; and a knowledge 

 of the laws of physics, and of the results of physical researches, 

 appears, therefore, essential for the successful prosecution of 

 engineering works. The very intimate relation of mechanical 

 science to mathematics and physics, and the indebtedness of 

 engineers to men of science outside the ranks of their own pro- 

 fession, are, indeed, evidenced by the roll of the Presidents of 

 .Section (J, containing the names of Dr. Robinson, ilr. Babbage, 

 Prof. Willis, I'rof. Walker, and Lord Rosse. 



Chemistry in A'l-ialion to Engiiieerini^. — f las-making is in 

 reality a chemical operation on a large scale, consisting in the 

 destructive distillation of coal, the purification and collection of 

 the resulting carburetted hydrogen, and the separation and 

 utilisation of the residual products. Chemistrj', accordingly, 

 holds a very important place in the requirements of the gas 

 engineer. 



The manufacture of iron, steel, and other metals, and the 

 formation of alloys, are essentially chemical operations ; and the 

 Bessemer and Clilchrist processes, by which steel is produced in 

 large quantities directly from cast iron, by eliminating a portion 

 of the carbon contained in it, and also the injurious impurities, 

 silicon and phosphorus, in place of the fonner costly and circuitous 

 method of removing the carbon from cast iron to form wrought 

 iron, and then combining a smaller proportion of carbon with 

 the wrought iron to form steel, are based on definite chemical 

 changes, and necessitated chemical knowledge for their develop- 

 ment. 



Chemical analysis is needed for determining the purity of a 

 supply of water, or the nature and extent of its contamination ; 

 and Dr. Clarke's process for softening hard water, by the addi- 

 tion of lime water, depends upon a chemical reaction. The 

 inethods, also, of purifying water by filtration, shaking up with 

 scrap iron, and aeration, are chemical operations on an extensive 

 scale ; and their efficiency has to be ascertained by chemical 

 tests. 



Cements and mortars depend for their strength and tenacity, 

 when mixed with water, uj^on their chemical composition and 

 the chemical changes which occur. The value of Portland 

 cement requires to be tested quite as much by a chemical 

 analysis of its component parts as by the direct tensile strength 

 of its bri(|uetles ; for an apparently strong cement may contain 

 the elements <jf its own disruption, in a moderate proportion of 

 magnesia or in an excess of lime. The chemical change which 

 has been found to occur in the Portland cement of very porous 

 concrete exposed to the percolation of sea-water under consider- 

 able pressure, by the substitution of the magnesia in sea-water 

 for the lime in the cement, if proved to take place even slowly 

 unfler ordinary circumstances, would render the duration of the 

 numerous sea works constructed with Portland cement very pre- 

 carious, and necessitate the abandonment of this very convenient 

 material by the maritime engineer. 



Explosives, which have rendered such important services to 

 engineers in the constrtiction of works through rock and the 

 blasting of reefs under water, as well as for purposes of attack 

 aiirl defence, form an important branch of chemical research. 

 The uses of gun-cott(m as an explosive agent, though not for 

 guns, have been greatly extended by the investigations of .Sir 

 Erederick .\bel, and by the discovery that it can be detonated. 



when wet and unconfined, by fulminate of mercury ; whilst 

 smokeless powder, a more recent chemical discover)', seems 

 likely, by its application to firearms, to produce important modi- 

 fications in the conditions of warfare. The progress achieved 

 by chemists in other forms of explosives has been marked by 

 their successive introduction for blasting in large engineering 

 works. Thus the removal of the rock in driving the >[ont 

 Cenis tunnel, in 1857-71, was effected by ordinary blasting 

 powder ; whilst the excavation of the longer St. Gothard tunnel, 

 in 1872-82, was accomplished by the more efficient explosive 

 dyn^mxle (Procetdiiif^s Inst. C.E.,\o\. xcv. p. 266). Moreover, 

 the ; first great blast for remo\-ing the portion of Hallett's Reef 

 which obstructed the approach to New York Harbour, was 

 effected mainly by dynamite, together with vulcan powder and 

 rendrock, in 1876 : whereas the far larger Flood Rock, in mid- 

 channel, was shattered in 1885 by rackarock, a mixture of potas- 

 sium chlorate and nitrobenzol, and a much cheaper and a more 

 efficient explosive underwater than (dynamite (Ibid., vol. xcv. 

 pp. 267-270). Rackarock is one of the series of safety explosives 

 first investigated by Dr. Sprengel in 1870, which, consisting of a 

 solid and a liquid, is safely and easily mixed for use ; and these 

 materials,' being harmless previously to their admixture, can be 

 stored in large quantities without risk (Journal of the Chemical 

 Society, August 1873). The cost also of this large blast 

 was greatly reduced by the .sympathetic explosion of the bulk of 

 the cartridges by the detonation of a series of primar)' exploders, 

 placed at intervals along the galleries and fired simultaneously 

 by electricity from the shore. 



The utilisation of sewage belongs to agricultural chemistry ; 

 and the deodorisation of sewage, and its conversion into a 

 commercial manure, are chemical processes. The disposal of 

 sewage by irrigation is a branch of agriculture ; and the innocuous 

 character of the effluent fluid, discharged into the nearest stream 

 or river, has to be ascertained by chemical analysis. Chemists 

 have the opportunity of benefiting the community, and at the 

 same time acquiring a fortune, by discovering an economical and 

 efficient process for converting sewage on a large .scale into a 

 profitable saleable manure, so that inland towns may not have to 

 dispose of their sewage at a loss, and that tow ns situated on 

 tidal estuaries or the .sea-coast may no longer discharge their 

 sewage into the sea, but distribute it jjroductively on the land. 



The purifying of the atmosphere from smoke, rendered in- 

 creasingly expedient by the growth of population, and the pre- 

 vention of the dense fogs caused by it, by some practical method 

 for more thoroughly consuming the solid particles of the fuel, 

 still await the combined efforts of chemists and engineers. 



Geology in Relation to Engineering. — A knowledge of the 

 superficial strata of the earth is important for all underground 

 works, and essential for tlie success of mining operation.s. 

 Geology is indispensable in directing the search for coal, iron 

 ore, and the various metals ; and the existence of faults or other 

 disturbances may greatly modify the conditions. The value of 

 geology to the engineer is not, however, confined to the extrac- 

 tion of minerals, for it extends, more or less, to all works going 

 below the surface. 



The water-supply of a district, in the absence of a suitable 

 river or stream, is dependent on the configuration and geology 

 of the district ; and the spread of London before the extension 

 of waterworks, as pointed out by Prof. Prestwich, had to be 

 confined to the limits of the gravel subsoil, in which shallow 

 wells gave access to the water arrested by the stratum of under- 

 lying London clay. The sinking also of deep wells for a supply 

 of water, and the depth to which they should be carried, are 

 determined by the nature of the formation, the ])osition of faults, 

 and the situation of the outcrop of the water-bearing stratum. 

 A geological examination, moreover, of a site proposed for a 

 reservoir, to be formed by a reservoir dam across a valley, has 

 to be made to ascertain the absence of fissures and the soundness 

 of the foundation for the dam. 



In the driving n{ long tunnels, the nature and hardness of the 

 strata and their dip, the prospects of slips, and the ixissibility of 

 the influx of large volumes of water, are geological con- 

 siderations which affect the designs and the estimates of cost. 

 The excavations also of large railway cuttings and ship canals 

 are considerably affected, both as regards their side slopes and 

 cost, by the nature and condition of the strata traversed. 



Meteorology in Relation to Engineering. — The maximum 

 pressure that may be exerted by the wind has to be allowed for 

 in calculating the strains which roofs, bridges, and other struc- 

 uires are liable to have to bear in expo.sed situations : and. con- 



NO. I 35 I, VOL. 52] 



