Prof. W. A. Norton on Terrestrial Magnetism. 



227 



Table XI 



Place. 



Temper atures. 



observed 



? 



Lat.63°,Lf»ii 93° W 



Lit. 55°, do. do. 



Lat 50°, do. do. 



IVhenioljes, 



Stretensk 

 Moscow, 



Ursa, . 



Berlin, . 



Washington, 



St, Louis, 



The Azores, 

 Havana, 



n 



4 



-6 6 



3 

 -5 



4 

 5 



6 



9 



n 



12 



i5 



i 22 



■5 



•3 



•o 

 •o 

 •o 



'9 



'7 



'9 



•6 



•6 

 ■5 



-8°- 



-2 • 

 2 • 



~7 



3 



4 



6 



8 



12 



i3 



16 -o 

 25 -o 



o 



•5 

 •5 

 •o 



•4 



•8 



"7 

 •o 



Diir. 



■H n: 4 



+o -8 



-f-2 -O 



+o -6 

 -fo - 9 



-o 



Temper atures. 

 MZZZ^observud, 



Diff. 



^1 



•2 



-a 



2 



-5 

 3-9 



3 



-2 ' 

 2 • 



O 



5 

 5 



Temperatures. 



§• otwervi 



W 



4 

 6 



4 

 4 



-o 



-o 



- 2 



4 



4 

 5 



9-4 

 ii -8 



12 -6 



i5 *9 



23 7 



-7 -o 



3 -o 



4 

 6 



8 



4 



o 



8 



+o°'9 

 -fo -3 



+o -4 



+i -4 

 +o «9 



o -o 



-b c -o -b°-o 



-2 -8 -a -5 



2 *5 2*5 



-6 -4 -7 

 3 -5 



Diff. 





o 



12 *7 



i3 *o 

 16 o 



25 -o 



4! 

 6 



-f-o 



-o 9 



- o -4 

 -o •! 



-i -3 



4 -i 



6 2 



9-3 



3 -o 



4 -4 

 6 -o 



8 -8 



ii *8! [2 -7 



j 2 -6 i3 -o 



i5 -6 16 -o 



24 -4 25 -o 



i 



O '-O 



- o 

 o 



-o 



-o -9 

 -o 



- o 

 -o-6 



3 

 o 

 6 

 5 

 3 



2 



5 



4 

 4 



Now making n =--■§, and making the calculations for various 

 latitudes north of 50°, I find that expressions (27) and (21) re- 

 main very nearly constant. The value of (21) does not vary 

 more than 0-01 from 50° to 60° of latitude. If we suppose n 

 to be a very small fraction greater than f, then (21) will decrease 

 from 50° northward. In fact, that (21 ) will decrease for n nearly 

 equal to unity may at once be seen by considering that, when 

 «=1, (21) is reduced to its numerator. 



For other meridians than 93°, or thereabouts, the diminutions 

 of cos b and cos b' are greater in going north, and thus (21) di- 

 minishes north of the point where 8+8' = 90, even for »=f 

 To determine the variation of (21) south of this point, we will 

 take the same expressions (25) and (26) as for the meridian ot 

 93 °. On either side of this meridian b and b' increases, but b is 



If we take the meridian for which 



continually greater than b. 



ft/ , at the point of 8+8' =90 , ~ -,-- ■ . ■< 



this meridian 8+8' varies for any change of latitude an amount 



is equal to 10°, it appears that on 



equal to about twice the latitude. This will be evident on com- 

 Paring the facts for the meridian of 93° with the statement that 

 for New York, for the meridian of which b> at the point above 

 ^ntioned is about 20°, 8 + 8' is equal to 10^° It follows, 

 therefore, that for the meridian assumed, 5° south of the point at 

 — - numerator of (26) is less than^sm 1» - 



,. Hence (26) 



iminishes SOUtll 



*hich 8 + 8 



'90481, while the numerator of (25) 

 — : [ f (26) is greater than 



(25). Whence it appears 



cos 10° 



from the point where 8+8* = 90*, or ^m very near th^por ot 

 P <* meridians at a distance from 93° a detailed calcnlatwjMB 



pessary to make out distinctly that (21) d irain ^ she ^h J the 

 ^ may avoid this calculation by establishing that south .<* the 

 gmts at wh i ch d+<r== 90°, (21) is greater for the meridian ot 

 J* (or rather for the meridian a little to the west ^ofrtus on 

 ^mch the angle between * and * is zero) than te*™^™™? 

 tK K at every considerable latitude. By making unfavorable 



% 



