heroes of the telegraph-第24章
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be found from the resistance observed。 The instrument formed the subject of the Bakerian lecture for the year 1871。
Siemens's researches on this subject； as published in the JOURNAL OF THE SOCIETY OF TELEGRAPH ENGINEERS （Vol。 I。； p。 123； and Vol。 III。； p。 297）； included a set of curves graphically representing the relation between temperature and electrical resistance in the case of various metals。
The electric pyrometer； which is perhaps the most elegant and original of all William Siemens's inventions； is also the link which connects his electrical with his metallurgical researches。 His invention ran in two great grooves； one based upon the science of heat； the other based upon the science of electricity； and the electric thermometer was； as it were； a delicate cross…coupling which connected both。 Siemens might have been two men； if we are to judge by the work he did； and either half of the twin…career he led would of itself suffice to make an eminent reputation。
The success of his metallurgical enterprise no doubt reacted on his telegraphic business。 The making and laying of the Malta to Alexandria cable gave rise to researches on the resistance and electrification of insulating materials under pressure； which formed the subject of a paper read before the British Association in 1863。 The effect of pressure up to 300 atmospheres was observed； and the fact elicited that the inductive capacity of gutta…percha is not affected by increased pressure； whereas that of india…rubber is diminished。 The electrical tests employed during the construction of the Malta and Alexandria cable； and the insulation and protection of submarine cables； also formed the subject of a paper which was read before the Institution of Civil Engineers in 1862。
It is always interesting to trace the necessity which directly or indirectly was the parent of a particular invention； and in the great importance of an accurate record of the sea…depth in which a cable is being laid； together with the tedious and troublesome character of ordinary sounding by the lead…line； especially when a ship is actually paying out cable； we may find the requirements which led to the invention of the 'bathometer；' an instrument designed to indicate the depth of water over which a vessel is passing without submerging a line。 The instrument was based on the ingenious idea that the attractive power of the earth on a body in the ship must depend on the depth of water interposed between it and the sea bottom； being less as the layer of water was thicker； owing to the lighter character of water as compared with the denser land。 Siemens endeavoured to render this difference visible by means of mercury contained in a chamber having a bottom extremely sensitive to the pressure of the mercury upon it； and resembling in some respects the vacuous chamber of an aneroid barometer。 Just as the latter instrument indicates the pressure of the atmosphere above it； so the bathometer was intended to show the pull of the earth below it； and experiment proved； we believe； that for every 1；000 fathoms of sea…water below the ship； the total gravity of the mercury was reduced by 1/3200 part。 The bathometer； or attraction…meter； was brought out in 1876； and exhibited at the Loan Exhibition in South Kensington。 The elastic bottom of the mercury chamber was supported by volute springs which； always having the same tension； caused a portion of the mercury to rise or fall in a spiral tube of glass； according to the variations of the earth's attraction。 The whole was kept at an even temperature； and correction was made for barometric influence。 Though of high scientific interest； the apparatus appears to have failed at the time from its very sensitiveness； the waves on the surface of the sea having a greater disturbing action on its readings than the change of depth。 Siemens took a great interest in this very original machine； and also devised a form applicable to the measurement of heights。 Although he laid the subject aside for some years； he ultimately took it up again； in hopes of producing a practical apparatus which would be of immediate service in the cable expeditions of the s。s。 Faraday。
This admirable cable steamer of 5；000 tons register was built for Messrs。 Siemens Brothers by Messrs。 Mitchell & Co。； at Newcastle。 The designs were mainly inspired by Siemens himself； and after the Hooper； now the Silvertown； she was the second ship expressly built for cable purposes。 All the latest improvements that electric science and naval engineering could suggest were in her united。 With a length of 360 feet； a width of 52 feet； and a depth of 36 feet in the hold； she was fitted with a rudder at each end； either of which could be locked when desired； and the other brought into play。 Two screw propellers； actuated by a pair of compound engines； were the means of driving the vessel； and they were placed at a slight angle to each other； so that when the engines were worked in opposite directions the Faraday could turn completely round in her own length。 Moreover； as the ship could steam forwards or backwards with equal ease； it became unnecessary to pass the cable forward before hauling it in； if a fault were discovered in the part submerged： the motion of the ship had only to be reversed； the stern rudder fixed； and the bow rudder turned； while a small engine was employed to haul the cable back over the stern drum； which had been used a few minutes before to pay it out。
The first expedition of the Faraday was the laying of the Direct United States cable in the winter of 1874 a work which； though interrupted by stormy weather； was resumed and completed in the summer of 1875。 She has been engaged in laying several Atlantic cables since； and has been fitted with the electric light； a resource which has proved of the utmost service； not only in facilitating the night operations of paying…out； but in guarding the ship from collision with icebergs in foggy weather off the North American coast。
Mention of the electric light brings us to an important act of the inventor； which； though done on behalf of his brother Werner； was pregnant with great consequences。 This was his announcement before a meeting of the Royal Society； held on February 14； 1867； of the discovery of the principle of reinforcing the field magnetism of magneto…electric generators by part or the whole of the current generated in the revolving armaturea principle which has been applied in the dynamo…electric machines； now so much used for producing electric light and effecting the transmission of power to a distance by means of the electric current。 By a curious coincidence the same principle was enunciated by Sir Charles Wheatstone at the very same meeting； while a few months previously Mr。 S。 A。 Varley had lodged an application for a British patent； in which the same idea was set forth。 The claims of these three inventors to priority in the discovery were； however； anticipated by at least one other investigator； Herr Soren Hjorth； believed to be a Dane by birth； and still remembered by a few living electricians； though forgotten by the scientific world at large； until his neglected specification was unexpectedly dug out of the musty archives of the British Patent Office and brought into the light。
The announcement of Siemens and Wheatstone came at an apter time than Hjorth's； and was more conspicuously made。 Above all； in the affluent and enterprising hands of the brothers Siemens； it was not suffered to lie sterile； and the Siemens dynamo…electric machine was its offspring。 This dynamo； as is well known； differs from those of Gramme and Paccinotti chiefly in the longitudinal winding of the armature； and it is unnecessary to describe it here。 It has been adapted by its inventors to all kinds of electrical work； electrotyping； telegraphy； electric lighting； and the propulsion of vehicles。
The first electric tramway run at Berlin in 1879 was followed by another at Dusseldorf in 1880； and a third at Paris in 1881。 With all of these the name of Werner Siemens was chiefly associated； but William Siemens had also taken up the matter； and established at his country house of Sherwood； near Tunbridge Wells； an arra
