May i6, 1878] 



NATURE 



81 



the genius and no less of the sagacity of Halley, he in part 

 follows Halley's view?, and considers that two magnetic systems 

 are directly recognisable in the phenomena of the magnetism of 

 the globe ; the one having a terrestrial, the other a cosmical 

 origin. The magnetism proper of the globe, with its point of 

 greatest attraction {i.e. in the northern hemisphere) in the north 

 of the American continent is the stronger ; the weaker system, 

 or that which results from the magnetism induced in the earth 

 by cosmical aciion, with its point of greatest attraction is, at 

 present, in the north of the Asiatic continent. Sir Edward 

 Sabine also expresses his belief that ' it is the latter of these 

 two systems which by its progressive translation, gives rise to 

 the phenomena of secular change, and to those magnetical 

 cycles which owe their origin to the operation of the secular 

 change.' ^ 



"Reviewing these several hypotheses by the light of observa- 

 tions made in recent years, it is difficult, and indeed in some 

 directions, impossible to recogiiise their accordance with changes 

 now going on : there can be no doubt, notwithstanding, that 

 Halley and Hansteen analysed their facts with skill, and that 

 their deductions were borne out by those facts. In explanation 

 of this anomaly it is necessary to glance retrospectively on the 

 changes in progress at the times in which these philosophers 

 gave utterance to their views [1700-1819]. During this long 

 interval, and, so far as relates to parts of the northern hemi- 

 sphere, for a century before, there was in the higher latitudes a 

 general movement of the north end of the needle in the following 

 directions : — 



"Over all that area (embracing the Atlantic and Indian 

 Oceans) from Hudson's Bay to about the meridian of the North 

 Cape o Europe, and from Cape Horn to about the western part 

 of Australia, the north end of the needle was successively drawn 

 to the west at a maximum rate of 8' or 10' a year. From the 

 meridian of the North Cape of Europe to that of 130° east, it 

 was^ successively drawn to the east, while from thence to Hud- 

 son's Bay it was nearly stationary, or perhaps oscillated a little : 

 in the southern hemisphere, from about the western part of 

 Australia to Cape Horn, the movement M'as throughout to the 

 east at the maximum rate of 7' a year. There was thus a 

 general uniformity of movement : in that hemisphere [dividing 

 the globe into eastern and western hemispheres] which includes 

 the Atlantic and Indian Oceanr, the needle was constantly 

 drawn more and more to the west ; in the hemisphere embracing 

 the Pacific Ocean, more and more to the east. 



"So far then to the early part of the present century we can 

 trace a harmonious movement of the needle over the whole 

 globe, justifying the conclusions of oiu" old philosophers ; but in 

 the year 18 18 at London, and generally contemporaneous with 

 that epoch throughout Europe and North Africa, the westerly 

 progress of the noi-th end of the needle ceared, and an easterly 

 movement commenced ; this continues to the present time, and 

 with a yearly increasing rate. But in the South Atlantic 

 during this period the westerly jmovement has never ceased ; it 

 is still going on, and in some parts with rapidity. Here, 

 then, is a marked dislocation of the harmonious regularity 

 embodied in Halley's and Hansteen's calculations and con- 

 ceptions. 



"The matured views of Sir Edward Sabine, to which I have 

 drawn attention, seem to anticipate the difficulties attendant on 

 this new and complex movement ; for, if I apprehend his mean- 

 ing correctly, they imply that the poles of attraction which 

 have a terrestrial source, i.e. the magnetic poles, are not subject 

 to translation.2 



" The hypothesis, if further followed, is nevertheless beset 

 with difficulties ; for we can scarcely conceive changes due to 

 cosmical action to be otherwise than general in character, and to 

 affect the whole globe. Thus, if the progressive translation of 

 the induced or weaker system in Northern Asia— and presumably 

 of that iii the southern hemisphere — were the direct causes of 

 the secular charges, we should anticipate uniformity in the 

 general movements of the needle as manifested by its variation 

 and dip over the earth's surface. But this is contrary to modern 

 experience ; for in some regions great activity of movement, 

 both in the direction of pointing and in the inclination of the 

 needle, is going on ; in others there is comparative repose in 

 both elements ; while in another region the needle remains nearly 

 constant in its direction, while its inclination sensibly varies from 

 year to year. For example : — 



I Phil. Trans., \Z(n, Art. v". ; iC63, Art. xii ; 1S72, Art. xv". 

 " So far as modern observatons bear on tbe po;ition of the magnetic poles, 

 they indicate permanency rather than change of place. 



"A region of remarkable activity presents itself in the South 

 Atlantic Ocean : a great part of the seaboard of South America 

 extending to Cape Horn, and including St. Paul's Rocks, 

 Ascension, St. Helena, and the Falkland Islands, with their 

 adjacent seas, are embraced therein. In some parts of this 

 area the westerly movement of the needle exceeds 7' or 8' a 

 year, and has so progressed for nearly three centuries. On the 

 American coast the dip of the south end of the needle decreases 

 from 7*5' to 4' yearly, while from the Cape of Good Hope to As- 

 cension it increases from 5' to 10' yearly. We have here, within 

 narrow limits, a noteworthy dislocation of the observed 

 phenomena. 



"Another region of activity, so far as is denoted by the 

 changes of variation, extends over Europe, Western Asia, and 

 North Africa. Here the needle, in opposition to the protracted 

 westerly movement going on in the South Atlantic, commenced 

 moving to the eastward in the early part of this century; it 

 has a progressive rate which in some parts now amounts to 10' 

 a year. The dip diminishes in this region seldom more than 

 3' a year. 



"A region of activity, so far as the dip is concerned, but with 

 little change in the variation, is to be found on the west coast of 

 South America ; at Valparaiso, as at the Falkland Islands, the 

 south dip decreases at the rate of 7' yearly, but in sailing north- 

 ward and reaching the loth degree of south latitude, this active 

 movement appears to cease. 



" But little activity in either element now exists over the 

 habitable part of the North American continent or in the West 

 Indies. Throughout China there is little change in the variation, 

 but an increasing dip of 3' or 4', and thus a reverse movement to 

 that going on in Europe. 



' ' Over a great part of the Western Pacific Ocean, as also 

 in Australia and New Zealand, there is so little change in the 

 two elements that this may be termed a region of comparative 

 repose. 



" These are a few facts relating to secular changes going on in 

 two magnetic elements within our own time ; and what are the 

 inferences to be drawn therefrom ? They appear to me to lead 

 to the conclusion that movements, certainly beyond our present 

 conception, are going on in the interior of the earth ; and that 

 so far as the evidence presents itself, secular changes are due 

 to these movements and not to external causes : we are thus 

 led back to Halley's conception of an internal nucleus or inner 

 globe, itself a magnet, rotating within the cuter magnetised 

 shell of the earth. 



"We need not here pause to discuss the probability of this 

 fanciful conception of the old philosopher, tut proceed to 

 examine how far the behaviour of another element, the intensity 

 of the earth's magnetism, confirms the view that movements are 

 going on in the interior of our globe. In common I believe with 

 all those who have pursued the study of this element from 

 the time when Sabine's original memoir to the British Asso- 

 ciation [1837] threw so much light on this special division of the 

 subject, I had conceived that stability, within very limited con- 

 ditions, was a distinctive condition of the earth's force ; and that 

 it was alone by watchful attention to the instrtunents of precision 

 devised for its determination that changes in short intervals of 

 time, such as a generation, could be detected. ^ If we turn to 

 the results obtained in this country through nearly half a cen- 

 tury, it is possible that an increase of two or three hundredths 

 of the total force may be found. In Italy at the present time 

 the annual decrease has been given by that active observer, the 

 Rev. Father Perry, as '004; so also on the North American 

 continent, where, as we are told by the zealous magnetician, 

 Schott, there is evidence of the force slightly increasing at 

 Washington, of being stationary at Toronto, in Canada, and 

 slightly decreasing at Key West, in the Gulf of Mexico. So 

 far stability, within very small limits, obtains over a very large 

 part of the northern hemisphere. If, however, we turn to the 

 continent of South America and its adjacent seas (parts of which 

 are regions of marked activity as denoted by changes in the 

 variation and dip of the needle), we shall find a diminution of 

 the intensity of the earth's force now going on in a remarkable 

 degree ; an examination of the recent observations made by the 



' The investigations of that able magnetician, Mr. Brcun, lead him to 

 consider that the earth's magnetic force increases and diminishes from day 

 to day by nearly the same amount over the whole globe. These increases 

 and diminutions have been traced to the action of the sun in such a way 

 that the greatest of them recur frequently at intervals of twenty -six days, 

 or multiples of twenty-?:;x d.ays — a fericdf]attributab!e tD the sun^s rctaUon. 



