Page:A Voyage of Discovery and Research in the Southern and Antarctic Regions Vol 1.djvu/183

] variation is rather further to the eastward than former observations would have placed it, and in opposition to the generally assumed progressive movement of the isogonal lines, from east to west in the southern hemisphere. It is, however, remarked by Professor Barlow, in his laborious investigation of this matter, in the Philosophical Transactions (for 1837, p. 671.), that this line of no variation, which passes through Australasia, has undergone very little change of position during these last sixty years; and it seems probable that the variation about this spot is as fixed as that on the coast of America. It would, however, be desirable, under favourable circumstances of weather, to repeat experiments on the variation at regular intervals of time, in order to ascertain whether a retrograde movement of the isogonal lines in these parts may not have begun, as our observations would seem to show; and as is well known to have occurred with those in England between twenty and thirty years ago.

We have also full reason to believe that at the Cape of Good Hope, where the westerly variation had been regularly increasing ever since about the year 1600, when the line of no variation passed through it, at the average rate of between seven and eight minutes annually, attained its maximum in 1840. By our observations in April of that year it amounted to 29° 14′ W., and those made at the Magnetic Observatory, since its establishment there by me at that time, and afterwards by