September 24, 1903] 



NATURE 



501 



lished from time to time; and the last, for the epoch 1902, 

 is based upon 8000 observations. 



There are other contributions to terrestrial magnetism for 

 positions on various coasts from the surveying service of the 

 Royal Navy, and our ships of war are constantly assisting 

 with their quota to the magnetic declination, or variation, 

 as sailors prefer to call it ; and wisely so, I trow, for have 

 they not the declination of the sun and other heavenly bodies 

 constantly in use in the computation of their ship's position? 



This work of the Royal Navy and the Indian Marine is one 

 of great importance, both in the interests of practical navi- 

 gation and of science ; for besides the equipment of instru- 

 ments for absolute determinations of the declination, dip, 

 and horizontal force supplied to certain of our surveying- 

 ships, every seagoing vessel in the service carries a landing 

 compass, specially tested, by means of which the declination 

 can be pbserved with considerable accuracy on land. 



Although observers of many other objects may still speak 

 of their " heritage the sea " as a mine of wealth waiting for 

 them to explore, unfortunately for magnetic observations we 

 can no longer say " the hollow oak our palace is," for wood 

 has been everywhere replaced by iron or steel in our ships, 

 to the destruction of accurate observations of dip and force 

 on board of them. Experience, however, has shown that 

 very useful results, as regards the declination, can be ob- 

 tained every time a ship is " swung," either for that purpose 

 alone, or in the ordinary course of ascertaining the errors of 

 the compass due to the iron or steel of the ship. 



As an e.xample of this method, the cruise of the training 

 squadron to Spitsbergen and Norway in 1895 may be cited, 

 when several most useful observations were made at sea in 

 regions but seldom visited. Again, only this year a 

 squadron of our ships, cruising together near Madagascar, 

 separated to a distance of a mile apart and " swung " to 

 ascertain the declination. 



I would here note that all the magnetic observations made 

 by the officers of H.M. ships during the years 1890-1900 have 

 been published in a convenient form by the Hydrographic 

 Department of the Admiralty. 



The fact remains, however, that a great portion of the 

 world, other than the coasts, continues unknown to the 

 searching action of the magnetic needle, whilst the two- 

 thirds of the globe covered by water is still worse off. 

 Amongst other regions I would specify Africa, which, apart 

 from the coasts. Cape Colony, and the Nile valley to lat. 

 5^° N., is absolutely a new field for the observer. 



Moreover, the elaborate surveys I have mentioned show 

 how much the result depend upon the nature of the locality. 

 I am therefore convinced that travellers on land, provided 

 with a proper equipment of instruments for conducting a 

 land survey of the strange countries which they may visit, 

 and mapping the same correctly, can, with a small addition 

 to the weight they have to carry, make a valuable contribu- 

 tion to our knowledge of terrestrial magnetism, commencing 

 with observations at their principal stations and filling in 

 the intermediate space with as many others as circumstances 

 will permit. 



The Antarctic Expedition. 



Of the magnetic work of our Antarctic expedition we know 

 that since the Discovery entered the pack — and, so far as 

 terrestrial magnetism is concerned, upon the most important 

 part of that work — every opportunity has been seized for 

 making observations. 



Lyttelton, New Zealand (where there is now a regular 

 fixed magnetic observatory), was made the primary southern 

 base-station of the expedition ; the winter quarters of the Dis- 

 covery, the secondary southern base-station. Before settling 

 down in winter quarters, magnetic observations were made 

 on board the ship during the cruise to and from the most 

 easterly position attained off King Edward VII. Land in 

 lat. 7b° S., long. 152^° W., and she was successfully swung 

 off Cape Crozier to ascertain the disturbing effects of the 

 iron upon the compasses and dip and force instruments 

 mounted in the ship's observatory. 



As a ship fitted to meet the most stormy seas and to buffet 

 with the ice, the Discovery has been a great success. Let me 

 add another tribute to her value. From Spithead until she 

 reached New Zealand but small corrections were required for 

 reducing the observations made on board. The experience 

 of Ross's Antarctic expedition had, however, taught the 



NO. 1769, VOL. 68] 



lesson that two wood-built ships, the Erebus and Terror, 

 with but some 3° to 4° of deviation of the compass at Simon's 

 Bay, South Africa, found as much as 56° of deviation at their 

 position farthest south, an amount almost prohibitory of 

 good results being obtained on board. 



How fared the Discovery? I have been told by Lieutenant 

 Shackleton — for the cause of whose return to England we 

 must all feel great sympathy — that a maximum of only 11° 

 of deviation was observed at her most southerly position. 

 From this we may look forward hopefully to magnetic re- 

 sults of a value hitherto unattained in those regions. 



At winter quarters, besides the monthly absolute observ- 

 ations of the magnetic elements, the Eschenhagen vario- 

 meters or self-registering instruments for continuously re- 

 cording the changes in the declination, horizontal force, and 

 vertical force were established, and in good working order 

 at the time appointed for commencing the year's observ- 

 ations. 



I may here remind you that some time previously to the 

 departure of the British and German Antarctic e.xpeditions, 

 a scheme of co-operation had been established between them, 

 according to which observations of exactly the same nature, 

 with the same form of variometers, were to be carried out at 

 their respective winter quarters during a whole year, com- 

 mencing March i, 1902. Besides the continuous observations 

 with the variometers, regular term-days and term-hours were 

 agreed upon for obtaining special observations with them at 

 the same moment of Greenwich mean time. Both expedi- 

 tions have successfully completed this part of their intended 

 work. 



To co-operate in like manner with these far southern 

 stations, the Argentine Government sent a special party of 

 observers to Staten Island, near Cape Horn, and the 

 Germans another to Kerguelen Land, whilst New Zealand 

 entered heartily into the work. In addition, similar observ- 

 ations were arranged to be made in certain British and 

 colonial observatories, which include Kew, Falmouth, Bom- 

 bay, Mauritius, and Melbourne ; also in German and other 

 foreign observatories. 



We have all read thrilling accounts of the journeys of the 

 several travelling parties which set out from the Discovery, 

 and of the imminent dangers to life they encountered and 

 how they happily escaped them except one brave fellow 

 named \'ince, who disappeared over one of those mighty ice- 

 cliffs, upon which all Antarctic voyagers descant, into the 

 sea. In spite of all this there is a record of magnetic 

 observations taken on these journeys of which only an outline 

 has yet been given. Anticipations of the value of these 

 observations are somewhat clouded when we read in one 

 report that hills " more inland were composed of granite 

 rock, split and broken, as well as weatherworn, into extra- 

 ordinary shapes. The lower or more outer hills consisted of 

 quartz, &c., with basaltic dykes cutting through them." 

 Consequently, we have to fear the effects of local magnetic 

 disturbances of the needle in the land observations, whilst 

 buoyed up with the hope of obtaining normal results on 

 board the ship. • 



Judging from some land observations which have been 

 received, it appears that considerable changes have taken 

 place in the values of the magnetic elements in the regions 

 we are considering, but when making comparisons we have 

 to remember the sixty years which have elapsed since Ross's 

 time, and that he had nothing like the advantage of steam 

 for his ships, or of instruments of precision like our present 

 ship Discovery. His ships also were, as we have already re- 

 marked, much worse magnetically, causing far more serious 

 disturbance of the instruments. Hence the changes we note 

 may not be entirely due to changes in the earth's magnetism. 

 The observations made by the officers of the Southern 

 Cros's at Cape .Adare in 1899-1900 *ilso contribute to this 

 question of magnetic change. 



The Magnetic Poles of the Earth. 



I will now refer to those two areas on the globe where the 

 dipping needle stands vertically, known as the magnetic 

 poles. The determination of the exact position of these areas 

 is of great importance to magnetic science, and I will just 

 glance at what is being done to solve the problem. 



Let us consider the North Pole first, the approximate 

 position of which we know best from observation. If one 

 were asked to say exactly where that pole has been in observ- 



