124 COSMOS. 



that the morning principal minimum of 8h. is not changed in 

 our northern zone by the earlier or later time of sunrise. 

 At the two solstitial periods, and the three equinoxes, at 

 which, conjointly with Oltmanns, I watched the horary 

 variations for 5 to 6 consecutive days and nights, T found 

 that the eastern turning point remained fixed between 

 7h. 45m. A.M. and 8h. 15m. A.M. both in summer and ir 

 winter, and was only very slightly anticipated by the earliei 

 period at which the sun rose.* 6 



In the high northern latitudes near the Arctic circle, and 

 between the latter and the pole of the earth's rotation, the 

 regularity of the horary declination has not yet been very 

 clearly recognised, although there has been no deficiency in 

 the number of very carefully conducted observations regard- 

 ing this point. The local action of the rocks and the fre- 

 quency of the disturbing action of the polar light, either in 

 the immediate vicinity or at a distance, made Lottin hesi- 

 tate in drawing definite conclusions in reference to these 

 turning hours, from his own great and careful labours, which 

 were carried on during the French scientific expedition of 

 Lilloise in 1836, or from the earlier results, that had been 

 obtained with much care and accuracy by Lowenorn, in 

 1786. It would appear that at Reikjavik, in Iceland, 64 8' 

 lat,, as well as at Godthaab, on the coast of Greenland, 

 according to observations made by the missionary, Genge, 

 the minimum of the western variation fell almost as in the 



55 Examples of the slightly earlier occurrence of the turning hours 

 are given by Lieutenant Gilliss, in his Magn. Observ. of Washington, 

 p. 328. At Makerstoun, in Scotland (55 35' N". lat.), variations are 

 observed in the secondary minimum, which occurs about 9 A.M. in the 

 first three and the last four months of the year, and about 7 A.M. in the 

 remaining five months (from April till August); the reverse being the 

 case at Berlin and Greenwich (Allan Broun, Observ. made at Makers- 

 toun, p. 225). The idea of heat exerting an influence on the regular 

 changes of the horary variation, whose minimum falls in the morning 

 near the time of the minimum of the temperature, as the maximum 

 very nearly coincides with maximum heat, is most distinctly contra- 

 dicted by the nocturnal motions of the needle, constituting the second- 

 ary min. and secondary max. " There are 2 maxima and 2 minima of 

 variation in the 24 hours, but only one minimum and one maximum of 

 temperature" (Relshuber, in Poggend. Annalen der Physik und Chemie, 

 Bd. 85, 1852, s. 416). On the normal motion of the magnetic needle 

 in Northern Germany, see Dove, Poggend. Annalen, Bd. xix, s. 364 

 374. 



