702 * TERRESTRIAL jSIA&NETISM. 



10. McClintock's Voyage of the " Fox." Hourly Observations 

 of Magnetic Declination at Port Kennedy in the Winter of 

 1858-59, and Results compared with Observations made at 

 Point Barrow in 1852-54. (Phil. Trans., 1863.) 



Port Kennedy is in lat. 72° (Y 49", and long. 94° 19' W. The 

 Observatory was built on a large hummock of old ice about 

 220 yards magnetic south from the ship and about 400 yards 

 from land. 



Ice was cut into blocks and built to enclose a space 7 feet 

 square. The roof was of loose planks covered and cemented by a 

 mixture of snow and water. A slab of marble placed on slabs of 

 ice in the centre of the room was adjusted and frozen to the ice. 

 The declinometer was mounted and levelled on a tripod table-top 

 on brass grooves, and the table was frozen to the slab and the brass 

 levelling screws to the table. 



The declinometer was supported on a point and steadied, and its 

 weight relieved by a silk thread, but it did not work satisfactorily 

 until the magnet was supported o?il?/ by the silk thread which had 

 been employed to relieve its weight. 



Within the observatory were only a wooden candlestick, a 

 copper lamp, and a board upon which the observation-paper was 

 fastened by copper tacks. 



Accumulations of snow-drift on one side or the other of the 

 observatory occasionally slightly altered the level of the ice and of 

 the instrument. 



Auroras were of frequent occurrence. 



The extreme easterly disturbances are found to occur approxi- 

 mately at the same absolute time at Port Kennedy and at Port 

 Barrow ; and the principal maximum of westerly disturbance at 

 the same local time at the two stations. The secondary maxima 

 of westerly disturbance do not agree, and are stronger at Port 

 Kennedy. The positions differ about four hours in time, and are 

 nearly in the same latitude, both being about 2° north, of the 

 magnetic pole. 



The mean value of the dip at Port Kennedy in October and 

 November was 88° 27' '4 N., and hence the horizontal force was 

 small. Notwithstanding this, it appears that the energy of the 

 disturbing force is greater at Point Barrow. 



It is also a fact that the aurora is very much more frequent at 

 Point Barrow than at Port Kennedy. 



At Port Kennedy the aurora is seen about one day in four. 

 At Point Barrow it was seen about six days in seven, which must 

 be considered in connexion with the fact that 1853-54 were years 

 of minimum disturbance, and 1858-59 were years of maximum 

 disturbance, so that many more might have been expected at Port 

 Kennedy. 



Several of the auroras at Port Kennedy were seen over a space 

 of water open throughout the winter towards the S.W. 



When the disturbances are eliminated it is found that the solar 

 diurnal variation produces a maximum easterly deflection mag- 



