Prof. W. A. Norton on Terrestrial Magnetism. 



215 



Table VI. 



Montreal, 



Dorchester, 

 Albany, 



Springfield, 



Providence, 



West Point, 

 New Haven, 



Princeton, 

 Philadelphia, 

 Washington, 

 Hudson, Ohio, 

 Cincinnati, 



Hor. Inton 



sity. 



computed, ob 



•453 

 •5c3 

 ♦498 

 •507 

 *5u 

 •5i8 



•520 



•535 



•54i 

 •56o 

 •521 



•555 



erved. 



DuT. 



Place. 



409 



48 1 

 482 



499 



5oi 



521 



5 07 

 54o 



549 

 5 7 6 



532 



5-6 



+ 

 + 

 + 

 + 



+ 



o44 

 022 



016 



008 



010 



00 3 



oi3 



00 5 

 008 



016 

 on 



021 



Prairie du CJiien, 



Dubuque, 



Louisville, 



St. Louis, 



Lat. 35°, E. coast 



of U. States, 

 Lat. 30°, do. 

 Lat. 25°. 



Hor. Intensity. 



observed. 



•5o5 



•5i6 

 •5 9 8 



•616 



computed. 

 492 



5oi 

 56 1 

 562 



Dilf. 



Lat. 20°, 

 Lat. 15°, 

 Lat. 10°, 



Lat. 5°, 

 Equator, 



do. 

 do. 

 do. 

 do. 

 do. 

 do. 



618 

 691 

 7 56 

 8i3 

 859 

 8 9 3 



914 

 921 



-665 

 • 7 53 

 •821 

 •872 

 •892 

 •919 



'9 r 7 

 •936 



oi3 

 oi5 

 037 



o54 



047 

 062 



o65 



059 



o33 

 026 

 oo3 

 oi5 



It will be observed that the differences are greatest between 

 the latitudes 15° and 35°. Bat the observed elements are less 

 accurately known between these limits, being obtained by esti- 

 mation. It would appear, however, that the supposition that 

 C=0 in formula (13) is incorrect. It will be seen that the de- 

 terminations for latitudes south of New York are almost all in 

 deficiency, while those for places north of New York are in ex- 

 More accurate results might accordingly be obtained by 

 ^btracting some number from 1 + cos 21 and l+cos2L. Table 

 V H 3 was calculated in this manner, or from the formula 



cess. 



Hor. intensity =H il^i 21 ^ 



l+cos2L-C 



(14.) 



different values were given to C for every different place. 

 se va lues were empirically obtained from the observed tem- 

 peratures in the following manner. Kaemtz in his Course of 

 eorology, furnishes the following table of mean temperatures. 



Tern 



perature. 



25 s 



20 

 15 



10 

 5 







Latitudes. 



East Coast of America. 





24° 21' 

 32 20 

 38 24 

 41 30 

 44 51 

 51 57 



West Coast of Europe. 



31 27 

 41 33 



52 



60 



3 



7 



66 4S 



th J ln = the data of the second column of this table, we find 



"at the difference between the temperature at the equator and 



temperature at a certain latitude varies as 1 - cos 2Iat. - C : 



that at two different latitudes, I and L, the differences are as 



-cos 2/ - C : 1 - cos 2L - C. The value of C changes more or 

 ies s if wp ^nn :.i c xu_ i„*....j„„ / „. t if we take L = 



38° 24 



2 40 o <7 e chan £ e eit her of the latitudes I or L. 

 4r oi'' ancl 8 ive successively to I the values 32° 20', 

 ho 0' 44^ 51/ 51 o 57 , we fi n d f or c the values -2 



> 



1 1 *222 

 •240/ If we take L=38 3 24' and / =41° 30', C 



