ftl A (i N E T I (' S D R V E i F P E N N S V I. V A XI A . 



51 



Magnetic Survey of L843. 



The trip in ls|:j occupied less than one month, and Bince the needles were 

 again vibrated after returning to Philadelphia, we adopt the same rate of change 

 as found in is K) and 1841, viz.: for the cylinder + 0.00127, and for the bar 

 + 0.00064. 



We have at Philadelphia — 



Time of 10 vibrations, reduced to 60°, cylinder 35\045, July 20, 1843. 



bar 36.914. 



In 1S4:>, at Toronto, the horizontal intensity in absolute measure was determined 

 by Lieuts. Lefroy and Younghusband at the magnetic observatory (see Mr. Schott's 

 report of Jan. 19, 1861, U. S. Coast Survey Report, 1861), and found to be 3.537, 

 hence by the above proportion Philadelphia becomes L172, a value in exccllenl 

 agreement with the other determinations at this place. 



If we compare with Montreal, we have Lieut. Lefroy's determination at St. 

 Helen's in 1843, 3.083, hence Philadelphia becomes 4.138, a value not quite so 

 accordant as that found from the comparison with Toronto. 



For the introduction of the absolute value tor the stations visited in I s in. we 



