TRANSACTIONS OF SECTION G. 785 



colourinj^ of lifjhts on their visibility is of interest in determining the shades of 

 colour to be uspd for sijrnals and sbip-ligbts, and also the relative power of the 

 lights required for didereiit colours to secure equal illuminating power. Distinc- 

 tions of colour nro essential in these cases; but for distinguishing lighthouses the 

 use of coloured glasses has been abandoned, on account of their impairing the light 

 emitted ; and the desired indication has been effected by varying the number and 

 duration of the tlaslies and eclipses in each lighthouse. The detection of colour- 

 blindness is of interest to engineers, as this physical inhrmity incapacitates men 

 from acting as engine-drivers, signalmen, or navigating seamen. The use of com- 

 pressed (lil-gas enables buoys and beacons to give a warning or guiding light for 

 about three months without requiring attention ; and the electric light has 

 accelerated the passage through the Suez Canal from ',]0^ hours to 20 hours, and 

 has greatly increased the capacity of the Canal for traffic by enabling navigation to 

 be carried on at night. The electric light also affords an excellent, safe, and cool 

 light in the confined cabins on board ship, in the headings of long tunnels, and in 

 the working-chambers filled with compressed air used for sinking subaqueous 

 foundations. 



Acoustics might se?m to have little relation to engineering ; but the soundness 

 of the wheels of a train are tested by the noise they give when struck with a 

 liammer; warning notes are emitted by railway and steamship whistles^ the fog- 

 horn on board ship, and the whistling and bell buoys employed for marking shoals 

 or the navigable channel ; whilst the striking of bells, the blast of steam sirens, 

 and the explosion of compressed gun-cutton cartridges and rockets indicate the 

 position of lighthouses in foggy weather. The most powerful sounds that can be 

 produced by the help of steam appear to have a very limited range as compared 

 with light; for, under ordinary conditions, the most powerful siren ceases to be 

 audible at a distance of six or seven miles; whilst the transmission of sound is 

 very much afiected by the wind and the condition of the atmosphere. It seems 

 possible that loud detonations at short intervals may be more readily heard than 

 the continuous blast of a steam trumpet. 



Electrical engineering is very intimately connected with physics, for it really 

 is the application of electiicity to industrial purposes. The very close relation 

 between electricity and magnetism, discovered by Oersted in 1820, and further 

 established by the remarkable researches of Faraday, has led to the present system 

 of generating electricity by the relative movement 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 little loss of energy ; and it can either be used directly for lighting 

 by arc or incandescent lamps, or be reconverted 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 1843, 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 applied 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 prose- 

 cation 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 profession, are, indeed, evidenced by the roll of the 

 Presidents of Section G, containing the names of Dr. Robinson, Mr. Babbage, Pro- 

 fessor Willis, Professor Walker, and Lord Rosse. 



Chemistn/ in Relation to Engineering . — Gas-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 separa- 

 tion and utilisation of the residual products. Chemistry, accordingly, holds a very 

 important place in the requirements of the gas engineer. 



1895 3 E 



