6. In this power to extend our expeditions without danger, and especially in sledge journeys during the autumn and spring, which are possible only to expeditions prepared to winter in the ice, are the grounds why we have not halted at the barriers “of the bulwarks built for eternity;” in the Rennselaer harbour, in the Lancaster-Barrow route, or at the Pendulum islands. It is only sledge expeditions, as Middendorf says, which have been able to effect results of any magnitude on the inaccessible coasts of the extreme north; and the great extent to which the Russians had used sledge expeditions evidently served as an example both to the English and to Kane. 7. In Polar expeditions, therefore, we have probably reached, so far as the exploration of the highest latitudes by means of ships is concerned, the limits of possibility. The extraordinary success which fell to the lot of Hall’s expedition _teaches us only the possibility of encroaching but a little beyond that limit_, even under the most favourable circumstances. 8. In all cases where the attempt shall be made to reach the highest latitudes with a ship, I would again recommend the route through Smith’s Sound, because, in the first place, I believe that any considerable advance is only to be expected in coast-water; and in the second place, because the Grant Coast offers facilities for sledge expeditions on a large scale. East Greenland in the higher latitudes, 73°-75°, may be regarded as inaccessible; and the attempt to penetrate northwards in its coast-water was a delusion of the second German North-Pole expedition. In the north of Spitzbergen, and in Behring’s Straits, fifty expeditions and countless whalers have heard from the ice an imperious _ne plus ultra_; and the same prohibition has been uttered to as many expeditions on the North-East passage. In both these routes the cause of failure was the disproportion between what could be reached in one or two summers, and the vast extent of sea blocked by impenetrable ice. In like manner, the probability of reaching the Pole itself with our present resources is so small, and the attempt to do it is so utterly disproportionate to the sacrifices exacted and the results achieved, that it would be advisable to exclude it from Arctic exploration, until, instead of the impotent vessels of the sea, we can send thither those of the air.