III. Account of magnetic observations made in the years 1858–61 inclusive, in British Columbia, Washington Territory, and Vancouver Island

Abstract

In 1858 a Commission was appointed for the purpose of determining and marking the forty-ninth parallel of north latitude from the Pacific to the Rocky Mountains. At the suggestion of General Sabine, this Commission was provided with a set of portable magnetic instruments adapted for the determination of the three magnetic elements, Dip, Declination, and Total Force. These instruments were similar in kind to those which had been used on the Magnetic Survey of the United Kingdom. Before delivery to the Boundary Commission they were examined at the Kew Observatory, and several constants and tables for facilitating the computations were determined and prepared there. The method of transporting the instruments from place to place, and indeed everything appertaining to the Boundary Commission, was by means of packet mules. Two boxes (a very light load for one mule) contained all the magnetic instruments, which throughout four years of such rough usage retained their original efficiency. Some of the needles became somewhat rusted; but I can suggest no alteration in the construction of such instruments, such as would increase their portability. The declinometer was, I think, unsatisfactory as regarded its capability of determining azimuths of the sun: when at an astronomical station, I necessarily had a meridian mark for the transit instrument, and I referred the direction of the magnet to such meridian.