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The scales of these maps vary, but an approximation can be made from the blue error lines. These are all very good determinations of longitude. Considering that they were made on-the-march, not means calculated from many observations at a station, they could hardly be better.

Charles Preuss, 0ct 10, 1843

"Half-passed ten in the evening. I am sitting alone by the fire to watch till twelve o'clock, when an immersion of satellites will occur. To tell the truth, I wish the dear Lord had not attached any satellites to Jupiter. One can loose one's mind over it. These immersions occur so often that one forgets how to sleep."

Near perfect determinations (above) at The Great Salt Lake.

The chronometer has lost time (above) between Aug 25 and September 21-24. But still very good determinations.

The results are even better (below) a few days later, because on Sept 18, he has had an opportunity to observe an emmersion of the first satellite of Jupiter in order to check the rate of his chronometer.

Theodore Talbot, Bent's Fort, August 16, 1845.

"Capt. F. has been much occupied with his transit Insmt. at which Mr. King assists him, & in other astronomical & meteorological obsnvs. in which I assist him. We are waiting here now for a moon culmination to determine the longitude of this place with the Transit Instrument."

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Bob Graham