2U 



Abstracts of Makerstoun Observations, 1843. 



Each of the four months gives nearly the same result. In the means of the months about the summer 

 solstice, there are two maxima and two minima, the diurnal curve is also double : — 



The minimum (as far as it can be deduced from the 9 observations), occurs at Noon, Makerstoun mean time. 



The maximum occurs about 6*^ 10™ p.m., 



A minimum occurs between 9'^ p.m. and S^ AM., 



A secondary maximum occurs about 8^ a.m., 



Whether the principal maximum occurs near noon or near midnight cannot be determined from the obser- 

 vations, but an examination of the monthly means ■will shew that the noon minimum becomes more marked from 

 January till June, and then becomes less so till December. 



The result for the whole year is exactly that for the equinoctial months. 



As the above results agree on the whole with those for the year 1844,* it may be permissable to con- 

 clude, that, — 



Is*, The diurnal curve is single in winter, unequally double at the equinoxes, and nearly equally double 

 at midsummer. 



2d, The minimum near noon occurs at the same hour in the equinoctial and summer months ; the morning 

 maximum occurs nearer noon in the equinoctial than in the summer months ; the principal or evening maximum 

 occurs nearly at the same hour in the winter and summer months, and farther from noon than in the equinoctial 

 months. 



In order to determine the period of the principal minimum, the observations made at 0™ on the term-days 

 of 1842 and 1843 have been used. The observations in 1842 were corrected by various temperature coeffi- 

 cients, depending on the method of deflections, the means in the following table were obtained after farther cor- 

 rections had been applied for the differences of the first coefficients from that obtained by comparisons of the 

 daily observations. The means in the following table are deduced from the term observations at 0™ in 1842 

 thus corrected, and, from the term observations in 1843, as corrected in this volume. The winter solstice includes 

 the months of November, December, January, and February, 1842 and 1843; the equinoxes, the months of 

 March, April, September, and October, 1842 and 1843 ; and the summer solstice, the months of May, June, 

 July, and August, 1842 and 1843. 



TABLE XIX. — Diurnal Variations of the Vertical Component of Magnetic Force, deduced from the 

 Observations at 0"" on the Term-Days of 1842 and 1843, the whole Vertical Component being 

 Unity. 



Hour. 



Winter 

 Solstice. 



Equinoxes. 



Summer 

 Solstice. 



1842. 



1843. 



Mean. 



Hour. 



Winter 

 Solstice. 



Equinoxes. 



Summer 

 Solstice. 



1842. 



1843. 



Mean. 





o-oo 



0-00 



0-00 



0-00 



0-00 



0-00 





0-00 



0-00 



0-00 



0-00 



000 



0-00 



10 



0250 



0572 



0299 



0492 



0281 



0357 



22 



0141 



0589 



0351 



0510 



0238 



0344 



11 



0190 



0532 



0256 



0410 



0267 



0309 



23 



0151 



0590 



0298 



0478 



0240 



0329 



12 



0080 



0420 



0153 



0292 



0170 



0201 







0184 



0552 



0241 



0460 



0218 



0309 



13 



0000 



0083 



0029 



0000 



0101 



0021 



1 



0220 



0517 



0233 



0478 



0194 



0306 



14 



0051 



0000 



0000 



0008 



0052 



0000 



2 



0229 



0510 



0288 



0500 



0211 



0326 



15 



0078 



0064 



0036 



0144 



0000 



0042 



3 



0225 



0556 



0359 



0547 



0238 



0363 



16 



0077 



0099 



0073 



0186 



0007 



0067 



4 



0251 



0671 



0382 



0622 



0274 



0418 



17 



0063 



0178 



0189 



0264 



0049 



0126 



5 



0248 



0729 



0401 



0632 



0313 



0443 



18 



0058 



0312 



0262 



0345 



0103 



0194 



6 



0228 



0783 



0425 



0638 



0345 



0462 



19 



0083 



0420 



0341 



0447 



0142 



0265 



7 



0227 



0788 



0441 



0661 



0336 



0469 



20 



0095 



0530 



0336 



0483 



0184 



0303 



8 



0197 



0707 



0473 



0632 



0313 



0443 



21 



0129 



0587 



0347 



0492 



0242 



0337 



9 



0194 



0604 



0448 



0563 



0293 



0399 



In the mean for all the periods, the principal minimum occurs at midnight, or l'^ a.m. In the mean for 

 both years, the principal minunum occm-s at I'* a.m. The principal minimum perhaps occurs nearer noon in 



* Transactions of the Royal Society of Edinburgh, Vol. XVI., p. 137. 



