TERRESTRIAL MAGNETISM. 403 



have Ix'come travelers to positions where the earth can carry on its 

 work on the needle undisturbed l>v electric trams and railways which 

 have sprung" up near theui, and it is to be hoped thej' will tind rest 

 there for man\^ years to come. 



Of the 42 observatories which publish the values of the magnetic 

 elements obtained there, 32 are situated northward of the parallel of 

 30 degrees north, and onl}- -i in south latitude; and it is a grief to 

 magneticians that so important a })osition as Cape Town or its neigh- 

 borhood does not make an additional fixed magnetic observatory of the 

 iirst order. 



Thus, as far as our present (Question of magnetic charts and their 

 compilation is concerned, the observatories do not contri1)utc largely, 

 but we should be very grateful to them for the accurate o})servations 

 of the secular change they providi^ which are so difticult to obtain else- 

 where. 



Of the value of magnetic charts for difi'erent epochs I huxe nuich to 

 sa}^ as they are requiret^l for purely scientific in<iuiry as well as for 

 practical uses. It is only b}- their means that we can realh' compare 

 the enormous changes which take place in the magnetism of the globe 

 as a whole; the}^ are useful to the miner, but consid(n-al)ly more so to 

 the seaman. Had it not been for the chart., compiled from the results 

 of the untiring labors of travelers by^ 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 sa}" 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 travelers In^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 geol- 

 ogy, l)otan3% zoology, and meteorology of the regions they visit, few 

 realize 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 inductiv<^ action of that great 

 parent magnet— the earth. 



How fares the compass on l)oard those magnets, the ships, that 

 instrument so indispensable to navigatioi\, wliich Victor Hugo has 

 forcibly called '* th(> soul of the ship,'' and of which it has been written, 



A rusted nail, placed near tiie faithful compaws, 

 Will sway it from the truth, and wreek an arffrwy. 



And if so small a thing as an iron nail Ite a danger, what are we to sa}^ 

 to the iron ship ^ Let us for a moment consider this imi)ortant matter. 



