Another light-hearted story by Ashley Sterne.
Punch, v149, p. 306
October 13, 1915
I had always thought that in order to make a map one had to be accompanied by a whole battery of theodolites, sextants, artificial horizons, spirit-levels, and logarithm tables. It was not until Petherby told me that all one required was a sheet of paper, a pencil and a compass, that the subject in all its naivete began to appeal to me.
Then one morning he came round to my house and proposed that we should spend the day in making a map of the neighbourhood. I explained to him that there already existed a highly ingenious plan of the district on view free at the railway station, which, besides indicating the principal thoroughfares and objects of historical interest, showed how, by changing trains only eleven times, it was possible to travel subterraneously from Bow Road to Golder's Green via Kennington Oval without ever coming up to (as the Londoners say) breave.
"We can do better than that," said Petherby, and we started.
We had some trouble at first with Petherby's compass. After spending the whole morning in making a map of the wild solitudes of Tooting Bee we discovered that the needle didn't point North. In fact, it had taken up a permanent sou'-sou'-westerly aspect. As a guide to the North Pole I would just as soon have employed a hot cross bun, or even Dr. Cook. I asked Petherby if he thought that the magnetic pole had through constant use lost its efficacy. But Petherby said no; it had not hitherto exhibited signs of exhaustion. Then I suggested to my friend that possibly he had omitted to wind the compass up over night and that it had run down. Petherby, on the other hand, suggested some unwarranted aspersions on my mental stability, and laid the blame of the disaster upon a biscuit-crumb which had worked its way in between the glass and the dial. If ever Petherby (usually the most orderly and punctilious of Special Constables) gets court-martialled and sentenced to be shot at cock-crow, it will be entirely owing to his deplorable habit of carrying his compass in the same pocket with his emergency rations.
The trouble being at length rectified we got to work in earnest, and the final results we achieved showed undeniably that whoever was responsible for the railway map was hopelessly out of the market by War Office reckoning. But then the poor fellow never had Petherby's advantage of attending lectures by an expert. He probably never knew that in order to get the correct relative positions of the Streatham tram-depot and the Brixton Bon Marclie, he ought to have lain down in the puddle outside the former and taken a fresh "North." I attribute my subsequent attack of gastric catarrh solely to my conscientious observance of this very necessary detail. But I bore my suffering bravely in the knowledge that the Bon Marche is really 347 paces easter than most people think. We discovered other discrepancies of a more or less serious nature, chief among which was the lamentable omission in the station map of the road in which the house was where those two pseudo-refugee ladies were found shaving one morning recently and — however, you know the story. I only mentioned it because the affair took place in the house of some friends of some friends of Petherby's, and thus I am in a measure personally connected with the episode.
On our way home late that afternoon Petherby drew my attention to a tall chimney. It belonged to a tea company, though I can't think why a tea-works should require a structure of such altitude, unless for the making of high tea.
"We'll come here to-morrow afternoon," said Petherby with enthusiasm, "and work out the height of that chimney. I 'm not quite sure how to set about it. It seems almost too severe a talk for the capabilities of a mere compass.
"How would it be," I suggested, "to give the compass a day off, and bring your aneroid? Then all we shall have to do will be to climb to the summit — somehow — and look at the instrument, when it will at once tell us how high we are above sea-level."
"How does it do that?" asked Petherby sarcastically. Does it chime the number of feet, or does a cuckoo emerge from a door in the dial and cuck it?"
"I don't know how it tells the altitude," I said, "but it does. Aeronauts always use one to calculate their height from the ground, and I daresay that 's how those Zeppelin chaps know when they 're low enough down to stand a chance of bombing a baby."
"I could have told them they were low enough down to do that without appealing to an aneroid," said Petherby.
"Of course," I continued, "the drawback is that if we make our observation at low tide we shall be much higher up than if we took it at high tide."
"I've got to attend a lecture to-morrow morning," said Petherby, " and I'll ask the lecturer for a simple homely recipe for calculating altitudes. Ten to one he'll know of some method which will be as easy as pie."
My own experience of pie is that it is almost invariably hard. I told Petherby so. And I said I could think of a very simple way.
"Well," said he on a note of irony, " if you can think of it between now and to-morrow afternoon I shall he obliged if you will let me know." I promised faithfully, and we parted.
By the last post that night I sent Petherby a brief note. "Never mind about asking your lecturer," I wrote. "The chimney's 78 feet high. After we separated I thought of a very simple way of making the calculation. I walked back to the tea-works and asked."