Magnet'wal Observatory of Dublin during the Years 1840-43. 83 



Table V. Ranges of the Declination in each month. 



It appears from the foregoing Table, that (as abo%^e stated) the greatest 

 range in summer is that of the westerly movement, its mean value being ll'-9 ; 

 while, in winter, the greatest range is that of the easterly movement, and its mean 

 value is 8'-3. It is remarkable, however, that the mean ranges of the easterly 

 and westerly movements, for the entire year, are precisely equal, the mean value 

 of each being 9'-l. 



The greatest value of the maximum range is that of April, and its amount 

 is 13'-3 ; the range then decreases imtil about the middle of July, and after- 

 wards increases, attaining a second, but smaller maximum in August. The 

 least value of the maximum range is that of December, and its amount is 6'-6, 

 being one-half of the greatest value. The mean value of the maximum range, 

 for the entire year, is lO'-l. 



The unexpected fact, of the occurrence of the greatest ranges in April and 

 August, was first noticed by Beaufoy. He seemed to think, however, that 

 the result was only an apparent one, and arose from the circumstance, that the 

 times of observation approached more nearly the epoch of greatest elongation 

 in April than in June. The fact has been since noted also by Gauss, in his 

 account of the Gottingen observations. " The differences" (of the declination 

 at 8 A. M. and 1 p. m.), he observes, " are not greatest at the time of the sum- 

 mer solstice, but appear smaller in June and July than in April, May, and 

 August ;" but he concludes, with Beadfoy, that this was due to the accidental 

 circumstance, that the whole range was not observed near the solstice, the time of 



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