NATURAL PHILOSOPHY. 125 



Capt. Maguire and his officers amused themselves with observing and 

 recording for seventeen months unremittingly the hourly variations of the 

 needle and the shifting scenery of the Aurora. Their observatory was the 

 sand of the shore with a dome of ice slabs lined with seal-skin fur. Their 

 instruments had come from Woolwich; their observations were as skilful 

 and exact as those of their fellow officers at Toronto, and their results have 

 been reduced, under the eye of the same master-mind in London, Major- 

 General Sabine, the highest authority living in this particular branch of 

 science. To the astonishment of all, these observations at Point Barrow 

 have turned out to be in some respects the direct reverse of those at Toronto. 

 While the regular solar declination of the needle follows the same law, the 

 needle bending furthest to the east and west at the same hours of the day at 

 both places, the disturbance diurnal variation at the one is just the opposite 

 of what it is at the other the west of one agrees with the east of the other, 

 and the east of the one with the west of the other, a difference the more 

 remarkable, since, at both places, there can be no doubt that the sun's heat is 

 the cause of the disturbance of the needle. At the same time the auroral 

 exhibitions keep time with the magnetic disturbances. Out of one thousand 

 seven hundred and eighty-eight hourly observations in three months of 

 1 8-3:2-53, four hundred and sixty-one showed an aurora; and out of one 

 thousand eight hundred and thirty-seven in the corresponding quarter of 

 the following year, six hundred and sixteen exhibitions of the aurora took 

 place. Six days out of seven, during these six months of night, the auroral 

 light replaced the sun light. For the first time, then, in the annals of me- 

 teorological science, the apparitions of this polar spectre have been studied 

 steadily and long enough to fix them to the different hours of the solar day, 

 and it is found that not a single record of their appearance was made 

 between eleven o'clock in the morning and three in the afternoon, whereas 

 one hundred and two are recorded at one o'clock at night. From this, their 

 favorite hour, their visits regularly decrease in number until midday, and 

 increase as regularly through all the evening hours up to midnight. But 

 this beautiful cycle of illumination for those polar wastes leaves us in total 

 darkness as to its hidden cause. And, to make perplexing conjectures more 

 perplexed, there seems to be a law of agreement between the frequency of 

 the auroras and the disturbances of the needle toward the west, but not 

 toward the east. 



ON THE INTENSITY OF THE TERRESTRIAL MAGNETIC FORCE. 



Mr. J. Drummond, in a communication to the British Association, 18;3S, 

 stated that, in comparing the observations of dip with those of intensity h- 

 had found some anomalous results, of which the following is an example 

 In the diurnal variation the dip is at a minimum about 8 A. M., at a maximum 

 about 11 A. M., after which it decreases to a minimum again about 2 p. M. 

 Turning now to the intensity, the maximum is found to occur about 8 A. M., 

 and the minimum about 11 A. M., after which it again increases, reaching a 

 maximum in the afternoon. From these facts, then, it would appear that, 

 while the earth exerts a greater attracting power over the needle about 11 A. M., 

 than either before that hour or after it, the intensity of the force by which 

 this is accomplished is then at its minimum. In other words, we are driven 

 to the conclusion, that the earth exerts a greater attracting power by a mini- 

 mum of force than by a maximum, a conclusion entirely at variance with 



11* 



