226 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



I would also draw attention to the fact, which the tables will show, that the usual 

 law which governs the variations in the declination of the needle does not obtain 

 between Fort Bridger and Genoa. At Bridger (longitude 110° 23' 47"), the declina- 

 tion obtains a maximum of 17° 30' E.; at Simpson's Spring (longitude 112° 47' 18"), 

 farther west, it declines to 15° 30' E.; and still farther west, at Genoa (longitude 119° 

 40' 30"), it again has increased to 16° 40' E. 



Mr. Francis A. Bishop, in his report on the Humboldt division of the Fort 

 Kearney, South Pass, and Hone}' Lake road, speaks of the same thing. His language 

 is: "It will be observed that the magnetic variation increases in going from the Honey 

 Lake (longitude 120° 15') to the City Rocks (longitude 113° 45') from 16° 00' 15" 

 E. to 17° 00' 20" E., contrary to the general law of magnetic variations.* 



Captain Whipple's table of magnetic results shows the like irregularity to obtain 

 • near the parallel of 35° of north latitude, between Albuquerque (longitude 106° 37' 

 52") and Soda Lake, the sink of the Mojave River (longitude 115° 58' 46"), though 

 not to the same degree, f 



The following is Lieutenant Putnam's communication, referred to above: 



Sir: Herewith is presented the results of observations for magnetic elements, en route from Fort Leavenworth to 



chronometer." These data were s 



uffloient, 



by means of a simple 





th polar distances 





>ute the true azimuth, 



■s the d< sired dec 









experiments of v 



.'.,-.- : 1 , I-- 



of deflection. 









which was suspended 



'is best done by t 



aoting the time o: 



F a large 



number of vibrations, 



n measuring the < 



angle n, through which the suspended magnet is 



and a certain distance from the fi 



L'St. 





and the formulas, 



»*=^* and ! 



j^=***t 



an w, (in which x is the 



then revolved l-ti around its vertical axis, and ends ot the needle road again; then the needle is om 



ibout its h.nger axi>, and r< ading taken as before. The same process precisely is gone through with a 



eraed, and the observation repeated with both. Whenever this 



h electrical state of the atmosphere, and to be certain that local attraction was not exerting any influence, I have 

 ■ passed over the same lines without experiencing any dimeulty, or witnessing any of the phenomena then so appa- 

 . I do not attempt to acconnt for the occ tu ena, but merely submit the facts in the case, although 



jpinion is that currents of electricity in the air had something to do in the case. 

 " Yours, very respectfully, 



" Wm. H. Paine. 

 " Capt. J. H. Simpson." 



* See Ex. Doc. No. 108, H. R., 35th Cong., 2d sess., p. 44. 

 t See Appendix " G," Pacific Railroad Reports, vol. iv. 



