1615.] Astronomical and Magnetical OLservatiom. 367 



Comparison of the Yearly Variation. 



April 



Jlay 



June 



July 



AiigU!.t . . . 

 September 

 October . . . 

 November. , 

 Derember . 

 January . . 

 February . 

 Marc!i 



Mean 



Difference. 



First 12 months observ. 



Morning. I Noon. Evening. 



09' 1«" 

 12 02 

 12 35 

 U 32 

 15 .55 

 15 4fi 

 15 41 

 1- 17 

 17 39 

 15 05 

 14 50 

 14 29 



21' 12' 

 20 54 



22 17 



23 04 

 23 32 

 22 32 



22 53 

 20 54 

 20 30 



19 03 



20 5S 



23 08 



24° 15' 

 24 13 

 24 16 

 24 16 

 24 16 

 24 16 



25" 



47 



04 



43 



08 



04 



24 15 33 



24 14 36 |24 21 42 24 15 41 



Second 12 months observ. 



Mean of the three difierences + SI" 



(To Dr. Thomson.) 



MY DEAR SIR, Hackney Wick, April 17, 1815. 



I HAVE the pleasure io send you the conclusion of the second 

 year's observations on the variation of the magnetic needle. The 

 number of observations made in the first year, and set down in the 

 Annals of Philosophy, were, in the morning 294, at noon 265, and 

 in the evening 141. But it is to be remarked that the numbers set 

 down are the means of the observations made with two needles, and 

 each consisting of 14 readings oil' on the arc of the instrument. If, 

 therefore, the former numbers be multiplied by 28, the total 

 amount will be IfKiOO, and tlie number in the second twelve 

 months will be found 22'J(JA. As every attention was paid In 

 making the observations, and the two needles rarely dillered three 

 minutes, seldom two, it n)ay be presumed that the variation is truly 

 determined, and has not yet arrived at its maximum, the annual 

 increase being 31". 



It certainly would be a desirable circumstance if observations 

 were made, at this period, in different parts of the world, especially 

 in tho<;e places where the variation is great : and as I perceive in 

 Number xxv. of the Annals of Philosophy, that Mr. Scoresby, jun. 

 of Whitby, ha^ kept meteorological journals during his voyages to 

 Davis's Stniils in the years 1813 and 1814, perhaps he, or some 

 other Gentleman, may favour your readers with observations on the 



