midday
`` We shall certainly have to do that ; but what interests me as much is , to know how far we have traveled . Can we also tell that by the sun ? '' `` Yes ; but to do so will depend on the accuracy of the observation . For the present , with only a single instrument , the bevel square , we must be content to make our calculations exactly at midday , when the shadow points due south . Or , in the northern hemisphere , when the shadow points due north . I want you , in the meantime , to think over that problem , as it is a very interesting one , and we will take it up when we are not so tired . '' It was a relief to get on fairly even ground again , where it would not be necessary to make turns and twists around all sorts of obstructions , to say nothing of ravines and water courses .