1 



622 



NATURE 



[April 26, 1900 



determinations of the orbit of the satellite to this planet have 

 been made during the period 1848-1898, but, owing to the 

 position of the planet and the plane of the orbit, many of the 

 earlier observations are very discordant, and it was only on 

 publication of the results obtained with the 26-inch at Wash- 

 ington that the certainty of change in the position of the orbit 

 plane was manifest {Washington Observations, 1873, 1881, 

 Appendix i.). Marth first drew attention to the changes as 

 being too great for systematic errors, but attempted no explana- 

 tion as to their cause {Monthly Notices, vol. xlvi. p. 504), and 

 finally Tisserand used his data to show that the phenomenon 

 could be explained by the assumption of a moderate polar com- 

 pression of the planet {Cotnptes rendus, vol. cvii. p. 804). In 

 calculating the perturbation Prof. Brown neglects the action of 

 the sun and other planets, as the chief effect is undoubtedly 

 due to the equatorial protuberance on Neptune itself He 

 therefore analytically obtains the elements of the satellite's 

 orbit with respect to the invariable plane of the planet's 

 equator, along which the node of the former moves with a 

 uniform retrograde motion, the inclination of the two planes 

 remaining constant. 



The variations of these elements at the various epochs then 

 furnish data for computing the annual motion of the node of 

 the orbit of the satellite on the equator of Neptune as seen from 

 the earth. The elements finally obtained indicate a period of 

 revolution of the node in 531 years. At the epoch 19000 the 

 position angle of Neptune's polar axis will be I58°'4, and the 

 plane of its equator will make an angle of -2i°'6 to the line 

 of sight. 



Taking the value i"'io as the most probable radius of the 

 planet from recent observations, and the mean distance of the 

 satellite as 16" '308, the flattening of Neptune is found to be 

 about 1/43. This would indicate a low mean density for the 

 planet, the value given being i '83 times that of water. 



THE RELATIONS BETWEEN ELECTRICITY 



AND ENGINEERING} 

 'T'HE nineteenth century is distinguished in our profession 

 -*■ chiefly by the knowledge we have obtained of the consti- 

 tution q{ matter 2,vyA of the qualities of the materials we utilise 

 for the service of man, of the presence and the characteristics 

 of that medium — the aether— which, fills all space, and of the 

 existence, indestructibility and protean character of that great 

 natural source of force, motion, work and power which we .call 

 — energy. 



Electricity is only one of many forms of this energy. It is 

 measureable in well defined and accurately-determined units. 

 It is produced and sold, utilised and wasted. It is, therefore, 

 something distinctly objective. It has even been defined by 

 Act of Parliament. There are four great principles underlying 

 the practical applications of electricity : — 



(i) The establishment of a magnetic field. 



(2) The establishment of an electric field. 



(3) The disturbance or undulation of the aether. 



(4) The work done by the generation and maintenance of 

 electric currents in material systems. 



Electricity as a science is fascinating to every one, but it is 

 deeply fascinating to the engineer. The trustworthiness of its 

 laws, the accuracy of its measurements, and the completeness and 

 definiteness of the units to which its measurements are referred 

 give him confidence in his estimates and a certainty of the per- 

 formance of his preconcerted operations. It places in his hands 

 the means of directing the energy out of sight in positions known 

 only to himself, and of applying it with great efficiency at the 

 exact spot desired. No magician or poet ever conceived so 

 potent a power within the easy reach of man. 



The Doing of Work. 

 The maintenance of an electric current through a conductor 

 means the expenditure of work upon that conductor, and this 

 expenditure of internal work means molecular motion. In solid 

 conductors the result is heat. If the current be gradually in- 

 creased, this motion is similarly increased. The result is suc- 

 cessively incandescence, white heat, fusion and disruption, 



1 Abridged from the "James Forfest " Lecture delivered at the Institution 

 of Civil Engineers, on April 23, by Sir William Henry Preece, K.C.B., 

 F.R.S. 



NO. 1 591, VOL. 61] 



In liquid conductors the motion probably becomes revolution. 

 The result is decomposition by the activity of the centrifugal 

 force ovelrcoming chemical affinity. The atoms fly away in fixed 

 determined lines, and collect at opposite poles. 



In gases the, transference of electric energy in the form of 

 sparks means dissociation. Compound gases are broken up into 

 their component elements under the same directing influences. 

 Work is done upon the gas as in the previous instances. 



The principle of work that lies at the very root of the pro- 

 fession of the engineer enables all these operations to be 

 measured in definite mechanical units, reducible to the common 

 English standard, the foot-pound, but which the electrical 

 engineer, with G;reater precision, refers to the scientific unit of 

 work — ihti Joit/e. 



The Purification of Matter. 



The elements and their useful compounds are rarely, if ever, 

 found pure. Impurities have to be sifted away. Ores, raw 

 produce, rocks and earths have to be subjected to various 

 processes of refining and conversion to extract from them that 

 which is wanted. The electric current by the above operations 

 has proved to be a powerful agent to break up crude materials 

 into their useful and useless constituents. The electro-chemical 

 industries of the world are very extensive. 



According to Prof. Porchers, the eminent electro-metallurgist, 

 the world manufacture of calcium carbide for the production of 

 acetylene gas is utilising a power equal to 180,000 HP. ; that 

 of the alkalies and the combinations of chlorine for bleaching, 

 56,000 HP. ; of aluminium, 27,000 HP. ; of copper, 11,000 

 HP. ; of carborundum, 2600 HP. ; and of gold, 455 HP. 

 P^lectroplating is one of the staple manufactures of Sheffield and 

 of Birmingham. There are nearly 200 firms working at the 

 former place, and over 100 at the latter. 



The decomposing bath and the arc furnace are revolutionising 

 many industries. Phosphorus is now being produced in England 

 in large quantities from corundum, and aluminium from bauxite 

 is extending in use and being reduced in price. The Post 

 Office is using aluminium for telephone circuits. I have recon)- 

 mended its use on a very large scale in the interior of Africa, 

 where transport is so costly. We can get the same conductivity 

 as with copper with half the weight, and at a less price, and we 

 can put up a line telegraphically ten times better than of iron 

 for less money. 



The Anmhilation of Space. 



The elements of Volta and the battery of Galvani — zinc, 

 copper and a solution of sulphuric acid — gave a convenient 

 generator of electric currents which could be directed along 

 wires to great distances, and thus, by establishing magnetic 

 fields, could deflect needles in such a way as to form the 

 alphabet and so transmit words and, therefore, thought. In 

 wires of great length, while the initial speed is that of light, it 

 takes time for the electric waves to rise and fall, so that the 

 number of currents which can be sent per second is limited. 

 Between London and Liverpool the speed of speaking is 

 virtually unlimited, but between Ireland and America it is 

 restricted by the so-called capacity of the cable submerged in 

 the ocean. This capacity absorbs energy and retards the rate 

 of rise and fall of currents. While a thousand currents per 

 second can be sent in the former case, only six per second are 

 available in the latter. 



Nevertheless, sitting on the shore of the Atlantic in Ireland, 

 one can manipulate a magnetic field in Newfoundland so as to 

 record simultaneously on paper in conventional characters 

 slowly written words. Thus we have bridged the ocean and 

 annihilated space. 



The regulation of the ever-growing traffic on our railways and 

 the safety of passengers is secured by similar means. The tele- 

 graph not only places the manager of the line in communication 

 with every station upon his system, but electric signals control 

 the motion of every train. A railway signal-box is an electrical 

 exhibition. Every line is protected by its own electric signal. 

 Every distant outdoor mechanical signal is repeated back. The 

 danger signal is locked, and cannot be losvered to " line clear " 

 until it is unlocked by the train itself or by the distant signal- 

 man. Mr. F. W. Webb is not only working the outdoor signals 

 themselves by electrical energy, but he is moving the points and 

 switches by the same means. So far, the experience gained at 

 Crewe during a period of about twelve months, from the working 

 of a signal cabin containing about sixty levers, has been such as 

 to justify confidence and the extension of the system, and some 



