504 



NA TURE 



[September 24, 1903 



Had it not been for the charts compiled from the results of 

 the untiring labours of travellers bj- land and observers at sea 

 in the field of terrestrial magnetism during the last century, 

 not only would science have been miserably poorer, but it is 

 not too much to say that the modern iron or steel steamship 

 traversing the ocean on the darkest night at great speed 

 would have been almost an impossibility, whereas with their 

 aid the modern navigators can drive their ships at a speed 

 of 26-5 statute miles an hour with comparative confidence, 

 even when neither sun, moon, nor stars are appearing. 



Of the large number of travellers by sea, including those 

 who embark with the purpose of increasing our geographical 

 knowledge of distant lands and busying themselves with 

 most useful inquiries into the geology, botany, zoology, and 

 meteorology of the regions they visit, few realise that when 

 they set foot on board ship (for all ships are now constructed 

 of iron or steel) they are living inside a magnet. Truly a 

 magnet, having become one by the inductive action of that 

 great parent magnet — the Earth. 



How fares the compass on board those magnets, the ships, 

 that instrurhent so indispensable to navigation, which Victor 

 Hugo has forcibly called " the soul of the ship," and of 

 which it has been written, 



" A rusted nail, placed near the faithful compass, 

 Will sway it from the truth, and wreck an argosy " ? 



And if so small a thing as an iron nail be a danger, what are 

 we to say to the iron ship? Let us for a moment consider 

 this important matter. 



If the nature of the whole of the iron or steel used in con- 

 struction of ships were such as to become permanently mag- 

 netic, their navigation would be much simplified, as our 

 knowledge of terrestrial magnetism would enable us to pro- 

 vide correctors for any disturbing effects of such iron on the 

 compass, which would then point correctly. But ships, taken 

 as a whole, are generally more or less unstable magnets, and 

 constantly subject to change, not only on change of geo- 

 graphical position, but also of direction of the ship's head 

 with regard to the magnetic meridian. Thus a ship steer- 

 ing on an easterly course may be temporarily magnetised to 

 a certain extent, but on reversing the ship's course to west 

 she would after a time become temporarily magnetised to the 

 same amount, but in the opposite direction, the north point 

 of the compass being attracted in each case to that side of 

 the ship which is southernmost. 



Shortly, we may define the action of the earth's magnetism 

 on the iron of a ship as follows : The earth being surrounded 

 by a magnetic field of force differing greatly in intensity and 

 direction in the regions from the North Pole to the Equator 

 and the Equator to the South Pole, the ship's magnetic con- 

 dition is largely dependent upon the direction of her head 

 whilst building and the part of that field she occupied at the 

 time ; partly upon her position in the magnetic field she 

 traverses at any given time during a voyage. 



For the reasons I have given, magnetic charts are a neces- 

 sity for practical purposes and in the following order of 

 value. That of the magnetic declination or variation which 

 is constantly in use, especially in such parts of the world as 

 the St. Lawrence and the approaches to the English Channel, 

 where the declination changes very rapidly as the ship pro- 

 ceeds on her course. Next, that of the dip and force, which 

 are not only immediately useful when correcting the ship's 

 compass, but are required in the analysis of a ship's mag- 

 netism both as regards present knowledge and future im- 

 provements in placing compasses on board. 



If astronomers have for a very long time been able to pub- 

 lish for several years in advance exact data concerning the 

 heavenly bodies, is it too much to hope that magneticians 

 will before long also be able to publish correct magnetic 

 charts to cover several years in .advance of any present epoch ? 

 If this is to be done within reasonable time there must be a 

 long pull, a strong pull, and a pull all together of magnetic 

 observers in all lands, and accumulated data must also be 

 discussed. 



On Magnetic Instruments for Travellers. 



Travellers in unsurveyed countries, if properly instructed 

 and equipped, can do good service to science by observing 

 the three magnetic elements of declination, inclination or 

 dip, and force at as many stations as circumstances will per- 

 mit ; hence the following remarks. 



For the purpose of making the most exact magnetic sur- 

 NO. 1769, VOL. 681 



vey the best equipment of instruments consists of the well- 

 known unifilar magnetometer, with fittings for observing 

 the declination, and a Barrow's dip circle. To some 

 travellers these instruments might be found too bulky, and 

 in some regions too delicate as well as heavy to carry. 



Of suitable instruments made abroad, those used by M. 

 Moureaux in his survey of France may be mentioned, as they 

 are of similar type, but much smaller and lighter than the 

 instruments above mentioned. 



Another form of instrument, called an L.C. instrument, for 

 observing both the inclination and total force, is shown in 

 the instrument before you. Originally designed for observ- 

 ations on board ships at sea where the ordinary magnetic 

 instruments are unmanageable, it has also been found to 

 give satisfactory results in a land survey, where greater 

 accuracy is expected than at sea. Thus, during a series of 

 observations extending from the north side of Lake Superior 

 to the southern part of Texas last year, comparisons were 

 made between the results obtained with an L.C. instrument 

 and those of the regular unifilar magnetometer and dip 

 circle, when the agreement was found satisfactory. 



■I am therefore of the opinion that a traveller furnished 

 with a theodolite for land-surveying purposes, but fitted with 

 a reversible magnetic needle, can at any time he observes a 

 true bearing obtain a trustworthy value of the declination. 

 Dismounting the theodolite from his tripod, the latter will 

 serve for mounting an L.C. instrument with which to ob- 

 serve the inclination and force. Thus, by adding to his 

 ordinary equipment an instrument weighing in its box about 

 21 lb., he can obtain valuable contributions to terrestrial 

 magnetism, and at the same time give useful assistance to 

 geological investigations. 



Concluding Remarks. 



Although a great subject like terrestrial magnetism, even 

 to exhibit our present knowledge of the science, cannot be 

 brought within the compass of an address — for it requires a 

 treatise of many pages — I have brought some of the broad 

 features of it before the Section in order to show its con- 

 nection with Geography. 



I also entertain the hope that geographers will become 

 more interested in a subject so important to pure science and 

 in its practical applications, and that it will become an addi- 

 tional subject to the instruction which travellers can now 

 obtain under the auspices of the Royal Geographical Society 

 in geology, botany, zoology, meteorology, and surveying. 



There is a wide field open to observers, and where results 

 often depend so much upon locality we require to explore 

 more and more with the magnetic needle. To look over the 

 great oceans and think how little is being done for terrestrial 

 magnetism is a great matter for regret. Vet even there we 

 may begin to be hopeful, for the United States Coast and 

 Geodetic Survey authorities are making arrangements to fit 

 out its vessels with the necessary instruments for determin- 

 ing the magnetic elements at sea. 



We wish them all success ; but I must again remind you 

 that although we cannot compel observers to start, there is 

 room for them and to spare. 



I would fain make some remarks on the prevailing 

 ignorance of sound geography in many quarters, and on the 

 defective methods of teaching the science ; but I feel that the 

 subject is placed in very able hands, and will be fully dis- 

 cussed elsewhere during the present meeting. 



SECTION G. 

 engineering. 



Opening Address by Mr. Charles Hawksley, Past 

 President Inst.C.E., President of the Section. 

 Since the last meeting of the British Association there 

 has passed from our midst, to the deep regret of all who 

 had the privilege of knowing him, one. who, though full 

 of years, actively followed his profession as a Civil Engineer 

 until within a few days of his death. I refer to Mr. Edward 

 Woods, who presided over Section G of the British Associ- 

 ation at Plymouth in 1877. Mr. Woods commenced his 

 professional career on the Liverpool and Manchester Rail- 

 way soon after it was opened for traffic. In 1875 Mr. 

 Woods was invited by the Royal Commission on Railway 

 Accidents to undertake, in conjunction with Colonel Inglis, 



