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Dr. T. E. Thorpe. 



mounted in the rear of the Tabernacle, was also placed at our dis- 

 posal ; and we had an opportunity of comparing our chronometers 

 with an instrument (Dent, 2392) which is regularly rated from 

 transit observations made by Mr. Anderson, of the President's Office. 

 Our next station was Ogden, in Northern Utah, at the observatory 

 directed by Lieutenant Wheeler, of the United States Engiueers, and 

 on the spot selected by the French astronomers for their observations 

 of the recent Transit of Mercury. The observatory was then in charge 

 of Professor Truman Safford, of Williams College, who also rated our 

 chronometers and otherwise did all in his power to facilitate our work. 

 The next stations were Green River in Wyoming, Grand Island in 

 Nebraska, Council Bluffs in Iowa, Chicago, Allegheny, and Wash- 

 ington. Washington is one of the best observed stations in the 

 States. Mr. Schott, of the United States Coast Survey Department, 

 who is well known as a leading magnetician in America, has here 

 made regular determinations in an observatory in the neighbourhood 

 of the Capitol Hill for many years past, and these he has tabulated 

 and discussed in various publications issued by the Coast Survey 

 authorities. My object in selecting Washington was to obtain an in- 

 dependent check on the indications of my instruments. Mr. Schott 

 was kind enough to allow me to set up my instruments in his obser- 

 vatory, and to afford me such assistance and information as I needed. 



I learned that the Coast Survey Department is gradually accumu- 

 lating data for a discussion of the magnetic history of the continent. 

 It has already published a map of declination for 1870, from which it 

 is evident that much has been done in the determination of this par- 

 ticular element since the date of Sir Edward Sabine's "Memoirs," 

 more especially along the Pacific slope and in the regions to the west 

 and south-west of the Great Salt Lake. As yet, however, no obser- 

 vations have been published relating to any of the districts west of 

 the Mississippi that we visited. 



The geographical positions of the several stations, their altitudes 

 above the sea-level, the geological character of the district in which 

 they are situated, together with such details of the exact sites as may 

 be necessary for their identification, are given in Table I. For the 

 greater part of the geological information I am indebted to my col- 

 league, Professor A. H. Green ; the rest I owe to the kindness of 

 General Humphreys, Chief of the United States Engineers, who sup- 

 plied me with the beautiful geological and topographical atlas accom- 

 panying Mr. Clarence King's Report of the Geological Exploration of 

 the Fortieth Parallel. 



I. Dip. 



The dip circles at my disposal were Barrow, No. 23, and Dover, 

 No. 6. The late Mr. Welsh had employed the former instrument in 



