694 



.TERRESTRIAL MAGNETISM 



The force in London, as determined by the same dipping needle, 

 being 100. 



The time of 100 vibrations in London was 6' 30" before the Ex= 

 pedition started, and 5' 36 • 5" after its return : giving a mean 

 value of 5' 33 -3". 



With regard to the diurnal changes in all the magnetic elements 

 contrary results were obtained at the two winter stations. 



At Winter Island the declination W., the dip and the force were 

 each greater in the morning than in the afternoon ; but at Igloolik 

 each of the three magnetic elements was gi-eater in the afternoon 

 than in the morning. 



At both stations the magnetic force increased as summer ad- 

 vanced. 



4. Parry's Journal of a Third Voyage for the Discovery of 

 a North- West Passage. (1824-25.) 



Magnetic Observations at Port Bowen. 



The dipping needles employed were three by Jones, 7 j inches in 

 length ; one of which, belonging to the same instrument, was em- 

 ployed for intensity, and to another each one of three brass spheres 

 could be attached, by means of which its moment of inertia could 

 be determined. .. , 



There were also two dipping needles by Dollond, one of whicn 

 was employed exclusively for intensity. 



•' The olDservations for intensity, by means of the time in which 

 the needles performed 100 vibrations in the meridian, are deduced 

 from the mean of 400 vibrations obtained with the face of the 

 instrument on each side of the vertical, and the needles reversed on 

 their axes in the two positions." 



These times are compared <vith the times during which the 

 same needle made 100 vibrations on '* Woolwich Common," at 

 11.30 a.m. on Dec. 3, 1825. 



Three observations for intensity were made at Port Bowen on 

 Nov. 8, 1824, Jan. 10, and June 27, 1825, and the ratio of the 

 force at Port Bowen to that at Woolwich was found to be 1 '296, 

 1*298, and 1*286 in the three experiments. 



The observations for the dip gave : 



Date. 



No. of 

 Observations^ 



Mean Dip. 



Nov. 1-12 - 

 Jan. 4-8 - 

 April 26, 27 

 June 2 - - 



June 27, 28 - 

 Aug. 30, 182.5 - 

 Dec. 4, 5, 1825 - 



10 

 6 

 3 

 3 



4 

 1 

 3 



Of// 



87 5 ^9^ 



88 05 31 1 Mean for all 

 88 13 02 }> the observations, 

 88 08 12 1 88° or 23^^ 



87 44 4lJ 



88 08 25 At Neill's Harbour. 

 70 4 At Woohvicli. 



