406 



Magnetic Declination. 



[June 16, 



XIII. " Note on a Comparison of the Diurnal Ranges of Mag- 

 netic Declination at Toronto and Kew." By Balfour 

 Stewart, LL.D., F.R.S., and William Dodgson. Received 

 June 9, 1881. 



Through the kindness of the Science and Art Department, South 

 Kensington, and of Mr. Carpmael, Director of the Toronto Observa- 

 tory, we have received daily values (excluding Sundays) of the diurnal 

 range of magnetic declination at Toronto. These observations extend 

 from 1856 to 1879 inclusive, thus forming a series of twenty- four 

 years. Each number is the difference in scale divisions of the declino- 

 meter between the greatest eastern and greatest western deflection of 

 the declination magnet on each day, as observed at the hours 6 a.m., 

 8 a.m., 2 p.m., 4 p.m., 10 p.m., and midnight, of Toronto mean time, one 

 scale division of the instrument being equal to 0''72 nearly. It is 

 probable that such differences represent very nearly the true diurnal 

 range. 



Disturbances appear to be violent at Toronto, and we have rejected 

 a few of the most disturbed observations, embracing those which 

 denote ranges above forty scale divisions, or 28' '8. In all 107 observa- 

 tions were thus rejected in the series of twenty-four years. Although 

 this rejection has been made, it must not be supposed that the remainder 

 are entirely undisturbed, but are only freed from the excessive influence 

 of a few violent disturbances. We have reduced in the meantime the 

 sixteen years extending from 1858 to 1873, in order to compare them 

 with a similar series of the Kew diurnal declination ranges, including 

 disturbances. 



The method of reduction has been precisely that adopted for the 

 Kew series, and already described by us (see " Proc. Roy. Soc," 

 No. 20, 1879, p. 313). 



Our object was to see whether there is any difference in phase 

 between the various Toronto and Kew inequalties, and for this 

 purpose we have adopted precisely the method formerly pursued by 

 ns when comparing together the declination ranges at Kew and 

 Prague (see "Proc. Roy^ Soc," vol. 29, p. 316). 



We have thus obtained the following result : — 

 Table 1. — Algebraic sum of Toronto and Kew Magnetic Inequalities. 



Toronto and Kew (Toronto 1 division to left) = 1545 14. 



(together) =161094. 

 ,, (Toronto 1 division to right) = 165016. 



2 „ ~ =165418. 



3 „ =161404. 



4 „ =154320. 



