The Worst Journey in the World - Apsley Cherry-Garrard (online e reader .txt) 📗

over which they glide: the sledge is running upon water. Crystals in such temperatures are larger and softer than those encountered in low temperatures. It is now that halos may be seen in the snow, almost reaching to your feet as you pull, and moving forward with you: we steered sometimes by keeping these halos at a certain angle to us. My experience is that the best pulling surface is at an air temperature of about +17° F: Wright’s experience is that below +5° during summer temperatures on the Barrier the surface is fairly good, that between +5° and +15° less good, and between +15° and +25° best. The worst is from +25° upwards, the worst of all being round about freezing point.

As the temperature became high the amount of ice melted by this sliding friction was excessive. It was then that we found ice forming upon the runners, often in almost microscopic amounts, but nevertheless causing the sledges to drag seriously. Thus on the Beardmore we took enormous care to keep our runners free from ice, by scraping them at every halt with the back of our knives. This ice is perhaps formed when the runners sink into the snow to an unusual depth, at which the temperature of the snow is sufficiently low to freeze the water previously formed by friction or radiation from the sun on to a dark runner.

In very low temperatures the snow crystals become very small and very hard, so hard that they will scratch the runners. The friction set up by runners in such temperatures may be known as rolling friction, and the effect, as experienced by us during the Winter Journey and elsewhere, is much like pulling a sledge over sand. This rolling friction is that of snow crystal against snow crystal.

If the barometer is rising you get flat crystals on the ice, if it is falling you get mirage and a blizzard. When you get mirage the air is actually coming out of the Barrier. Thus far Wright’s lecture.

Since we returned I have had a talk with Nansen about the sledge-runners which he recommends to the future explorer. The ideal sledge-runner combines lightness and strength. He tells me that he would always have metal runners in high temperatures in which they will run better than wood. In cold temperatures wood is necessary. Metal is stronger than wood with same weight. He has never used, but he suggests the possible use of, aluminium or magnesium for the metal. And he would also have wooden runners with metal runners attached, to be used alternately, if needed.

The Discovery Expedition used German silver, and it failed: Nansen suggests that the failure was due to the fact that these runners were fitted at home. The effect of this is that the wood shrinks and the German silver is not quite flat: the fitting should be done on the spot. Nansen did this himself on the Fram, and the result was excellent. [I believe that these Discovery runners were not a continuous strip of metal but were built up in strips, which tore at the points of junction.] Before it is fitted, German silver should be heated red hot and allowed to cool. This makes it more ductile, like lead, and therefore less springy: the metal should be as thin as possible.

As runners melt the crystals and so run on water, metal is unsuitable for cold snow. For low temperatures, therefore, Nansen would have wooden runners under the metal, the metal being taken off when cold conditions obtained. He would choose such wood as is the best conductor of heat. He tried birch wood in the first crossing of Greenland, but would not recommend it as being too easily broken. In the use of oak, ash, maple, and doubtless also hickory, for runners, the rings of growth of the tree should be as far apart as possible: that is to say, they should be fast growing. Ash with narrow rings breaks. There is ash and ash: American ash is no good for this purpose; some Norwegian ash is useful, and some not. Our own sledges with ash runners varied enormously. The runners of a sledge should curve slightly, the centre being nearest to the snow. The runners of ski should curve also slightly, in this case upwards in the centre, i.e. from the snow. This is done by the way the wood is cut. Wood always dries with the curve from the heart towards the outside of the tree.

During our last year we had six new Norwegian sledges twelve feet long, brought down by the ship, with tapered runners of hickory which were 3¾ inches broad in the fore part and 2¼ inches only at the stern. I believe that this was an idea of Scott, who considered that the broad runner in front would press down a path for the tapered part which followed, the total area of friction being much less. We took one of them into South Bay one morning and tried it against an ordinary sledge, putting 490 lbs. on each of them. The surface included fairly soft as well as harder and more rubbly going. There was no difference of opinion that the sledge with the tapered runners pulled easier, and later we used these sledges on the Barrier with great success.

If some instrument could be devised to test sledges in this way it would be of very great service. No team of men can make an exact estimate of the run of their own sledge, let alone the sledge which your pony or your dogs are pulling. Yet sledges vary enormously, and it would be an excellent thing for a leader to be able to test his sledges before buying them, and also to be able to pick out the best for his more important sledge journeys. I believe it can be done by attaching some kind of balance between the sledge and the men pulling it.

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