A Magnetic Survey of the Fortieth Parallel. 149 



determination on September 8, 1878, was 3° 42' - 85 (uncorrected for 

 diurnal range). 



In a later publication " On the Secular Change of the Magnetic 

 Declination in the United States and other parts of North America " 

 (United States Coast Survey Report for 1874, Appendix No. 8), Mr. 

 Schott adopts the formula 



D=l°-79 + l°-90 sin (l'5m + 5 -9), 



where m is the number of years and fraction of a year since 1850 ; 

 but this expression also affords lower values than those actually ob- 

 served. The value for 1880, for example, is given as 3° 15'"6, and for 

 1870 as 2° 54'. Mr. Schott has also discussed (loc. cit.) the various 

 observations made at New Haven, Connecticut, since 1761, and 

 has represented them by the expression 



D= +7-83 + 316 sin (l'4m-21°-6), 



where m has the same signification as in the last formula. The 

 annual change is at. present about 4^3. This would give for 1878'6 

 the value 8° 45', which agrees very closely with that actually observed. 



Sir Edward Sabine's collections afford the following data for further 

 comparison : — 



Diff. of Yearly 



Date. Decimation. Date. Declination, epoch. Change. 



o / o / Years. , 



Salt Lake City .. 1850 15 34 E. 1878-7 16 48 E. 2S7 -2-6 

 Pittsburg ..1840-5 08 W. „ 2 21 W. 38'2 + 3'5 

 ..1845-5 33 W. „ 2 21 W. 332 +3-3 



At Salt Lake City I was informed by Mr. Orson Pratt, who led the 

 first band of Mormons into Utah, that he had determined the magnetic 

 declination on what is now the site of the Mormon Tabernacle, and he 

 was so good as to afford me the following extract from his journal : — 

 " July 30, 1847. I took several observations during the day of the 

 sun's azimuths and altitudes, and by means of seven calculations I 

 ascertained the variation of the magnetic needle to be 15° 47' 23" E. 

 Instruments, sextant and ordinary azimuth compass." 



In concluding, I wish to tender my thanks to the various officials 

 connected with the public service in America with whom I came 

 in contact, for the prompt and courteous manner with which all 

 our requirements relating to the magnetic work were met. To 

 General Smith, commanding at Fort Lyon, in Colorado, we were in- 

 debted for the loan of a tent w^hich was placed at our disposal during 

 the whole of our journey : Rear- Admiral Rodgers, the Director of the 

 United States Naval Observatory at Washington, furnished us with 

 maps and letters, and procured us special facilities from certain of 

 the railroad companies, and otherwise showed his interest in the work. 



