

REPORT ON THE MAGNETICAL RESULTS. 11 



Horn focus. Here the needle was being drawn downwards at an annual rate of 1 1'. 

 The minor focus, showing a value of 4' in the annual change, the needle being drawn 

 downwards, was found in China, near Hong Kong. It must, however, be distinctly 

 understood that the positions thus described, with the values of change given, have only 

 an approximate value, and that only the general features of the distribution of change 

 in the angular direction of the freely suspended needle are to be accepted as clearly 

 shown by this investigation. 



If we may j udge by analogy of the changes going on in the Atlantic and its sea- 

 boards, there should be a focus of considerable decrease in the vertical force in the 

 neighbourhood of the assigned position of the north magnetic pole between the focus of 

 declination change in the German Ocean and that in Alaska ; but the suggestion will 

 not be followed further at present. The small map (Plate II.), showing the general 

 direction of the changes which were in progress during the years 1840-80, may perhaps 

 be consulted with advantage in illustration of the preceding remarks. 



In this map the regions of no secular change in the declination are shown by 

 continuous lines, and the peculiar trend of the line from Sitka to Magellan Strait, 

 following so nearly the general direction of the coast, is remarkable. The foci of 

 maximum change are marked by circles containing a number giving the amount, and 

 the attached arrow shows the direction, i.e. when the arrow is shown as deflected to 

 the right of the true meridian, the north-seeking end of the needle is moving to the 

 eastward, and when deflected to left, to the westward. The other arrows similarly show 

 the general direction in which the needle is moving. The foci of maximum change in 

 the inclination are marked by circles containing a number showing the amount, the 

 sign + signifying that the north end of the needle is moving downwards, and the sign 

 — the contrary movement. 



With regard to the maps of secular change in the earth's magnetic intensity, 

 although some remarkable points of interest are shown, they fall short in their value 

 as an approximation to the truth as compared with the other elements, — the declina- 

 tion values having been much longer and generally observed, and next to it the 

 inclination. 



In the horizontal force the more remarkable features were, the small annual 

 change near Cape Horn, about — 0"002 (B.U.), the focus of greatest change amounting 

 to — '01 7 between Valparaiso and Monte Video, and the gradually diminishing values 

 on the American continent until a zero line is met, starting from the great North 

 American lakes, across the Atlantic south of Bermuda, to the Cape de Verde Islands. 

 This decreasing annual change apparently extended across the Pacific Ocean in 

 diminishing value to Tahiti, over the South Atlantic to Southern Africa, and across 

 that continent to the east coast. 



To the northward and eastward of this zero the annual change showed signs of 



