“What! have you been so long at sea with me and never heard yet about the magnetic pole?”
“Never a word, father. It seems to me that poles are multiplying as we get further north.”
“Oh, Benjy, for shame—fie! fie!”
“Maybe if you had told me about it I might have had less to be shamed of, and you too, father.”
“That’s true, Benjy. That’s true. You’re a sharp boy for your age. But don’t be disrespectful to your father, Ben; no good can ever come o’ that. Whatever you are, be respectful to your old father. Come, I’ll tell you about it now.”
It will have been observed by this time that little Benjamin Vane was somewhat free in his converse with his father, but it must not therefore be supposed that he was really insolent. All his freedom of speech was vented in good humour, and the Captain knew that. There was, indeed, a powerful bond not only of affection but of sympathy between the little delicate boy and the big strong man. They thoroughly understood each other, and between those who understand each other there may be much freedom without offence, as everybody knows.
“You must understand,” began the Captain, “that although the needle of the mariner’s compass is said to point to the north with its head and to the south with its tail, it does not do so exactly, because the magnetic poles do not coincide exactly with the geographical poles. There are two magnetic poles just as there are two geographical poles, one in the southern hemisphere, the other in the northern. D’ye understand!”
“Clear as daylight, father.”
“Well, Benjy, the famous Arctic discoverer, Sir James Ross, in 1832, discovered that the northern magnetic pole was situated in the island of Boothia Felix, in latitude 70 degrees 5 seconds and longitude 96 degrees 46 seconds West. It was discovered by means of an instrument called the dipping needle, which is just a magnetised needle made for dipping perpendicularly instead of going round horizontally like the mariner’s compass. A graduated arc is fitted to it so that the amount of dip at any place on the earth’s surface can be ascertained. At the magnetic equator there is no dip at all, because the needle being equally distant from the north and south magnetic poles, remains horizontal. As you travel north the needle dips more and more until it reaches the region of the north magnetic pole when it is almost perpendicular—pointing straight down.
“Now, it is only on a very few places of the earth’s surface that the horizontal needle points to the true north and south, and its deviation from the earth’s pole in its determination to point to the magnetic pole is called the variation of the compass. This variation is greater or less of course at different places, and must be allowed for in estimating one’s exact course. In our present explorations we have got so far beyond the beaten track of travel that greater allowance than usual has to be made. In fact we have got considerably to the north of the magnetic pole. At the same time we are a good way to the east’ard of it, so that when I see the compass with its letter N pointing to what I know to be the magnetic north, I take our geographical position into account and steer almost due east by compass, for the purpose of advancing due north. D’ye see?”