120 COSMOS. 



minimum at 8 A.M. ; the first maximum at 2 P.M. ; the 

 second minimum at 12 P.M. or 2 A.M. ; and the second 

 maximum at 2 A.M. or 4 A.M. I must here content my- 

 self with merely giving the mean conditions, drawing atten- 

 tion to the fact that the morning principal minimum of 8h„ 



Freiberg, 1829. Breslau, 1835. Greenwich, 1346-47. 



Maximum 1 P.M. 1 P.M. 2 P.M. 



Minimum 1 A. M. 10 P. M. 12 P.M. 



Maximum 4 A.M. 4 A. M. 4 A.M. 



Minimum 8 A.M. S A.M. 8 A.M. 



Makerston, 1842-43. Toronto, 1845-47. Washington, 1840-42. 



Maximum Oh. 40m. 1 P. M. 2 P. M. 



Minimum 10 P.M. 10 P.M. 10 P.M. 



Maximum 2h. 15m. A.M. 2 A.M. 2 A.M. 



Minimum 7h. 15m. A.M. 8 A. M. 8 A. M. 



The different seasons exhibited some striking differences at Green- 

 wich. In the year 1847 there was only one maximum (2 P.M.) and 

 one minimum (12 night) during the winter ; in the summer there was 

 a double progression, but the secondary minimum occurred at 2 A.M. 

 instead of 4 A.M. (p. 236). The greatest western elongation (princi- 

 pal maximum) remained stationary at 2 P.M. in winter as well as in 

 summer, but the smaller or secondary minimum fell, in 1846, as usual 

 (p. 94), at about 8 A.M. in the summer, and in winter about 12 at 

 night. The mean winter western elongation continued, without inter- 

 mission, throughout the whole year between midnight and 2 P.M. (sec 

 also for 1845, p. 5). We owe the erection of the •observatory at Mak- 

 erston, Roxburghshire, in Scotland, to the generous scientific zeal of 

 Sir Thomas Brisbane (see John Allan Broun, Obs. in Magnetism and 

 Meteorology made at Makerston in 1843, p. 221-227). On the horary 

 diurnal and nocturnal observations of St. Petersburg, see Kupffer, 

 Compte-rendu Meteor, et Mag. a Mr. de Brock en 1851, p. 17. Sabine, 

 in his admirable and ingeniously combined graphic representation of 

 the curve of horary declination at Toronto {Phil. Transact, for 1851, 

 pt. ii., plate 27), shows that there is a singular period of rest (from 9 

 to 11 P.M.) occurring before the small nocturnal western motion, which 

 begins about 11 P.M. and continues till about 3 A.M. "We find," he 

 observes, " alternate progression and retrogression at Toronto twice in 

 the 24 hours. In two of the eight quarters (1841 and 1842) the infe- 

 rior degree of regularity during the night occasions the occurrence of 

 a triple maximum and minimum ; in the remaining quarters the turning 

 hours are the same as those of the mean of the two years." (Obs. 

 made at the Magn. and Meteor. Observatory at Toronto, in Canada, vol. 

 i., p. xiv., xxiv., 183-191, and 228 ; and Unusual Magn. Disturbances, 

 pt. i., p. vi.) For the very complete observations made at Washing- 

 ton, see Gilliss, Magn. and Meteor. Observations made at Washington, 

 p. 325 (General Law). Compare with these Bache, Observ. at the 

 Magn. and Meteor. Observatory at the Girard College, Philadelphia, made 

 in the years 1840 to 1845 (3 volumes, containing 3212 quarto pages), 

 vol. i., p. 709; vol. ii., p. 1285; vol. iii., p. 2167, 2702. Notwith- 

 standing the vicinity of these two places (Philadelphia lying only 1° 4' 

 north, and 0° T 33" east of Washington), I find a difference in tho 

 lesser periods of the western secondary maximum and secondary min- 

 imum. The former falls about lh. 30m., and the latter about 2h. 15m. 

 earlier at Philadelphia. 



