APPENDIX B. — GEOGRAPHICAL POSITION. 303 



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 City and Bridger's Fort, the loss of 1631 upon 

 its companion was 52, and 29.5 sec. on two respective days; on 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 lon- 

 gitude. They can be 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 jour- 

 ney. Their rates were given at Philadelphia. At Fort Leaven- 

 worth 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 de- 

 rangements do not obtain and affect these instruments merely while 

 moving, but that it is gradually recovered from when returned to 

 permanent rest. 



J. W. Gunnison, Lieut. Top. Engs. 



In charge of Astronomical Department. 



Capt. H. Stansbury, Top. Engs. 



Commanding Expedition to Great Salt Lake. 



