96 



The Rev. S. J. Perry on 



[Mar. 22, 



The angular value of one division of the scale of the vibration-magnet 

 No. 3 =2'-3. This was again tested at the Cape of Grood Hope, and 

 found to be 2' 16"*7. The same magnet had for its induction- coefficient 

 0*0002204, and its dimensions of inertia were the following : — Length 

 0-31736 foot, diameter 0-032681 foot, and weight 979-127 grains. 



The correction to 35° Fahr. was 



0-0001583 (*-B5 o )+0-00000046o (t— 35 ) 2 ; 

 and log 7v 2 k at 60° Fahr. =1-675300. 



Our chief astronomical station at Kerguelen was Observatory Bay, a 

 little to the south of the north-west corner of Royal Sound, its approxi- 

 mate latitude being 49° 25' ll"-9 S., and its longitude 4 h 39 m 34 s -3 E. 

 of Greenwich. At this station a long series of observations of the dip, 

 horizontal force, and declination were taken during our four months' 

 stay. The trips undertaken for the establishment of our two secondary 

 stations at Swain's Haulover and at Thumb Peak, and also for the longi- 

 tude connexions, afforded opportunities of observing the magnetic elements 

 at the second and third British stations, as well as at that of the Americans 

 at Molloy Point. The existence of a magnetic observatory at the G-erman 

 station rendered unnecessary any further observations at Betsy Cove. A 

 brick pier was erected on a solid foundation at Observatory Bay for the 

 magnetic instruments, and most of the observations were made on this 

 spot. 



The Magnetic Dip. 

 The dip observations were taken with three needles, and the results 

 obtained on different days are all entered in the following Table : — 



Observatory Bay 

 Swain's Haulover 

 Thumb Peak 



Observatory Bay 



1874-75. 



November 13.. 

 December 13 . . 

 December 21 . . 

 December 23 . . 

 January 13 .. 

 January 30 .. 

 February 18 .. 



No. 1. 1 No. 2. 



No. 3. Mean 



O / ill o i n o i no 



72 4 1 72 5 15 72 4 38! 



70 59 58 71 3 2 70 57 10 71 3 



171 6 38; 71 6 38' 



;71 57 6 71 54 30 71 55 48 



!71 52 40 71 56 54 71 54 47^ 



71 58 30 71 54 2172 3 34:71 58 48' 



71 42 



71 42 6: 



The station at Swain's Haulover was six or seven miles to the south 

 of Observatory Bay, and Thumb Peak about the same distance due east 

 of the Haulover. At Thumb Peak there was only time to observe with 

 a single needle ; the weather, too, was bad, and the spot chosen not very- 

 favourable, being on the shingle near the water's edge. The readings on 

 January 30th were taken on the rocks near the landing cove. The last 

 observation at Observatory Bay was made near the top of the rock over- 

 hanging the dwelling, and in a rather unsteady position ; it is therefore 

 less reliable than the others. The true dip for January 1st, 1875, at 

 Observatory Bay wiT probably be a little in excess of 71° 55' 13"-4, 

 which is the mean of the observed values. 



