1877.] 



Range of Magnetic Declination, 



115 



has therefore been obtained from Table I., and when applied to (B) we 

 obtain the following result : — 



Phase of lunation... (0) (1) (2) (3 (4) (5) (6) (7) 

 Corrected value of] c _ trvs 



winter range ) W "4" '4^ "409 "40s -409 -411 '408 (C) 



Series (C) is represented in Fig. XL (p. 120). 



10. If we now make use of the observations corresponding to the six 

 months grouped around the summer solstice (100 in all), we obtain the 

 following results :— 



Phase of lunation... (0). (1) (2) (3) (4) (5) (6) (7) 



Y rXe 0f . SU . mm . er } ' 621 ' 6GI ' 587 ' 6l ° ' 6 ° 4 ' 582 ' 591 (D) 



and if we apply to this a residual correction analogous to that applied to 

 (B), we obtain as follows : — 



Phase of lunation... (0) (1) (2) (3) (4) (5) (6) (7) 

 Corrected value of j ^ , 6qq g g6 . fi . 6 ^ 6 (E) 



summer range .J J ' ■ y T J 7 x ' 



In series (E) we have well-marked maxima corresponding to new an d 

 to full moon. 



E. Variations ivhich seem to depend on Planetary Configurations. 



11. From art. 6 we may conclude that the connexion between solar 

 spotted areas and declination-ranges is an intimate one. JSTow Messrs. 

 De La Hue, Stewart, and Loewy, in a paper already quoted (Phil. Trans. 

 1870), have shown that the amount of spotted area of the sun's surface 

 exhibits a reference to the chief planetary configurations. It becomes, 

 therefore, a question of interest to ask whether declination-ranges exhibit 

 a reference of the same kind*. 



In order to reply to this I have selected those configurations which 

 occur most frequently, and which might therefore be supposed to be suffi- 

 ciently well indicated by sixteen years' observations. 



These are, (a) the period of conjunction of Yenus and Mercury, (j3) the 

 solar period of Mercury, (y) the period of conjunction of Yenus and 

 Jupiter. 



In the next place, three-monthly values for every week have been con- 

 structed after the manner indicated in Table III. Xow inasmuch as the 

 periods of the three configurations already alluded to are not very far 

 different from three months, we may imagine that these three-monthly 

 values are to a great extent free from any inequality depending on these 

 periods. The differences between the monthly and the three-monthly 

 values will, however, exhibit any such inequality as may exist. These 



* Mr. C. Chambers, of the Bombay Observatory, has discussed the question as to 

 whether certain other magnetic elements have a reference of this kind (Phil. Trans. 

 1875, p. 361). 



12 



