Preparation for what we intended to attempt was not to be made without some thought, or at all events I do not find such preparation a perfectly simple matter. It requires exact calculation. The first thing is to make a list—in this case a list of all we should require at Camp IV, with the approximate weights of each article. But not every article would be available to be carried up on the first of the two journeys to the North Col; for instance, we must keep our sleeping-bags for use at Camp III until we moved up ourselves. It was necessary, therefore, to mark off certain things to be left for the second journey, and to ascertain that not more than half of the whole was so reserved. It might be supposed that the problem could now be solved by adding up the weights, dividing the total by ten (the number of our porters), and giving so many pounds, according to this arithmetical answer, to each man for the first journey. In practice this cannot be done, and we have to allow for the fallibility of human lists. However carefully you have gone over in your mind and provided for every contingency, you may be quite sure you have omitted something, probably some property of the porters regarded by them as necessary to salvation, and at the last moment it will turn up. The danger is that one or two men will be seriously overloaded, and perhaps without your knowing it. To circumvent it, allowance must be made in your calculations. On this occasion we took good care to carry up more than half of what was shown on our list on the first journey. Another difficulty in the mathematical solution is the nature of the loads. They cannot be all exactly equal, because they are composed of indivisible objects. A tent cannot be treated like a vulgar fraction. The best plan, therefore, is to fix a maximum. We intended our loads to be from 25 to 30 lb. They were all weighed with a spring balance, and the upper limit was only exceeded by a pound or two in two cases, to the best of my remembrance.