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Thi' AhuuJiitc Ohi^erration.'f. — As soon as possible the .absolute values of Declination, Horizontal Force, and 

 Inclination were determined, the instruments employed throughout the two years being the same, viz., 

 Unifilar >ragnetonieter No. 25 by Em.iott Bugs., and Inclinometer No. 27 by J. Dovek. All the magnets 

 were adjusted in their stirrups for the latitude, and foi' the Horizontal Force observation Magnet 2^)\ was 

 generally employed. The results of the observations show how constant the moment of this magnet 

 remaineil. The silk suspension threads were the same throughout, and were never once broken or 

 changed. 



The method of observation was the same as that employed at Kew and <.)ther observatories, the only 

 dirt'erenee being that, instead of distances 30 centims. and 40 centims., in the deflection experiment 

 42 centims. and 56 centims. were used, owing to the small size of the force. 



Magnetically disturbed days, especially in the summer, were very frequent. It was only on a few days 

 in each month that good absolute observations were possible. It was not always easy to select quiet days. 

 Frequently attempts at absolute observations had to be abandoned on account of too great disturbance, 

 and, in the winter, sometimes on account of a blizzard, which made intercourse l)etween the ship aiid 

 the shore, and observing in the small exposed alisolute house, almost impossilile. 



Ohervations for Local Attradkm. — In order to determine the influence of the rocks at the Observatory on 

 the absolute values, a large tent was erected on the unbroken sea-ice in jNIcMurdo Sound in November of 

 1903, 1-7 miles from the nearest shore line and over a spot where the depth of water was 200 fathoms 

 (1200 feet). Soundings showed the water to deepen quickly from 2 fathoms at Hut Point to 180 fathoms 

 a mile further out in the Sound to the west, while 10 miles away to the west-north-west the sounding was 

 100 fathoms. The deepest sounding was 400 fathoms, at a point 2 miles south-east of Observation Hill, 

 and other soundings showed that the water was much deeper to the south and to the south-east than to 

 the north and north-west of Winter Quarters. 



The Sound, therefore, may be taken to be 40 miles wide, with an average depth of 200 fathoms. The 

 ship when anchored in Winter Harbour had 9 to 11 fathoms of water, while on the north side of Hut 

 Point the water quickly deepened to 50 fathoms close in to the land. Hut Point itself is continued half 

 a mile to the south-west below water, in a shoal which gives soundings of from 2 to 25 and 40 fathoms. 



Three sets of observations were taken, viz., on November 4, 6, and 8. The results dift'er considerably 

 from those taken on shore, and indicate a larger dip and a smaller value for the Horizontal Force, whilst the 

 Declination seems less easterly. These observations were the standard sets taken as being most 

 undisturbed, and used as the base to which all the observations on board the " Discovery " were 

 reduced. 



The establishment of the Absolute House out on the sea-ice, although perhaps possible during the second 

 year, would have been attended by considerable difficulty and some risk, especially as it would have been 

 fully exposed to the heavy winter storms, and the surface of the ice, being hard and smooth, offered very 

 little holding ground. During the first year practically nothing was known of the ice conditions in the 

 Sound ; indeed, up to quite late in the year the ice within a few hundred yards of the ship was continually 

 breaking up and drifting away. 



Observations Across Barrier. — The tent on the ice was also made the base station for the observations 

 taken on the Ice Barrier sledge journey of November 10 to December 10, 1903, with Inclinometer No. 27 

 by J. Dover, having two reversible Inclination needles and two Total-Force needles. The farthest point 

 reached was about 155 geographical miles south-east of Mount Erebus. The geographical positions of the 

 " camps " were determined, whenever possiljle, by means of sextant observations of the sun in an artificial 

 mercury horizon. 



With the exception of those taken on November 28, all the magnetic observations were taken in the 

 evenings between 7 p.m. and 9 p.m., after the day's march. On two occasions only was it possible to 

 observe in the open air. In most cases the strong cold wind with drifting snow prevented open-air 

 observations, and they were then taken in the small, low sleeping tent, while the other two occupants 

 waited outside. These observations ought to give some indication of the rate of ch.-uigc over an apparently 

 undisturbed area in these latitudes. 



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