[Illustration: DIAGRAM OF THE NORTH MAGNETIC POLE REGION.]
The observations for dip, naturally the most important of the survey, will be made with a Kew Dip Circle employing two needles; the usual reversals of circle, face, and polarity should be attended to at each station, to place the instrument in the plane of the magnetic meridian. The usual method of finding the plane of the meridian will probably not answer in that part of the world for want of sufficient accuracy; the direction of the magnetic meridian should, therefore, be taken as indicated by the delicately suspended needle of the declination instrument, and, where this method fails, dip observations should be made in any two planes 90° apart, of which the first plane is preferably that of the meridian as guessed at.
It is proposed to charter a steam whaler to take the party from St. John's, Newfoundland, to the northern part of Repulse Bay, which, being directly connected with Hudson's Bay, is the nearest point to the pole-containing area that is accessible any year. There a permanent station is to be erected where regular observations will be continued all the time and from which each spring a field party (perhaps two) will start to locate the geographical position of the pole.
It may be well to repeat that the Magnetic Pole is that point where the needle of the dip circle is absolutely vertical--where it stands at exactly 90° to the plane of the horizon.
To find this unknown spot the observer follows as nearly as possible the direction indicated by the delicately poised needle of the declinometer. The magnetic meridian is not always a straight line, and may therefore indicate a very circuitous route, but by a system something like the regular approaches to a besieged fort one may be certain of arriving there eventually.
For instance, when the needle indicates a dip of 89° the stations should be nearer together--say not farther apart than twenty miles, if possible, and these intervals should be less as the dip increases.
Suppose the observer to have reached a point where the dip is found to be 89° 30´, and at the next station he has 89° 35´, at the next 89° 40´. At the next he may find only 89° 37´; he then returns to where he found the greatest dip and starts off at right angles, one way or the other, to that course. As long as the dip continues to increase, he knows he is travelling in the right direction. When it again decreases he returns to the point of his last greatest dip and travels at right angles to his last course as long as the dip increases. In this way he will eventually see the absolute verticity of the suspended needle marked and know he has reached the North Magnetic Pole at last. Sir James Ross did not succeed so well, the needle marking only 89° 59´ of verticity. But as this would indicate that he was within one and a quarter to two miles of the point sought, he was justified in feeling elated at his success.