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Show APPENDIX B.- GBOOBAPHICAL POSITION. 803 disregarded, the instruments used being too imperfect for such work. On the return journey the chronometers were carried in panniers on the most gentle mules. Their comparison exhibits " jumps and stops* so great as to forbid this mode of conveyance. Between Salt Lake Qity and Bridget's Fort, the loss of 1631 upon its companion was 52, and 29.5 sec. on two respective days; oft the last day's travel 1961 stopped entirely, and at the arrival at Fort Laramie, 1631 was 23 minutes in advance of the time of starting. There can be no doubt that light balanced pocket chronometers are best suited to this method of determining difference of longitude. They can bet put on spiral springs with suitable packing, in boxes, and strapped so as to ride horizontally on the body of the mounted man. The chronometer should be put into its place after the carrier has mounted, ( if on horseback,) and taken out by the astronomer at the halting, before alighting. But what is of great importance, the travelling rate of the instrument should be found previous to commencing the journey. This could be done by having it transported, in the manner intended on the route, the average daily number of hours, at the place of fitting out. With three well- tested chronometers, much confidence might be placed in their work, and if either one varied the others would detect it. Three^ persons should carry them. A remarkable fact is shown by those chronometers in our journey. Their rates were given at Philadelphia. At Fort Leavenworth they . both had the same relative rate, but had increased from less than one to ten seconds gain, having been transported in stages over the mountains. After being some months stationary, in the winter at the Salt Lake, they together returned to nearly the rates at Philadelphia. It would appear, therefore, that such derangements dp not obtain and affect these instruments merely while moving, but that it is gradually recovered from when returned to permanent rest. J. W. QUNOTSON, Lieut. Top. Hngf$. In charge of Aetronomieal Deportment. CAPT. H. STANSBURY, Top. Eng' 9. Commanding Expedition to Great Salt Lake. |
