EXPLANATION OF TAHLKS OF IIOCK'LY VALI'KS. 



EXPLANATION OF TABLES OF HOURLY VALUES. 



I'ages 8 to 70 contain tables giving the hourly values of Declination, Horizontal Force and Vertical 

 Force at Winter Quarters (lat. 77 50' 50" S., long. 166 44' 45" E.). The way in which these values 

 were arrived at is explained later (r (!|iap. III., 20). 



As a rule, each page contains data for a single month for one of the elements, but November ami 

 December, 1903, and January, 1901, contained so few days of registration that a single page sutliced for 

 these three months. The time shown in these tables is local mean time, which was llh. 7m. fast on 

 Greenwich. As is usual in magnetic tables, there appears at the top of the Declination tallies a value in 

 degrees common to all the hourly values, and at the top of the Horizontal- and Vertical-Force tables the 

 commencing figures or figure of the values expressed in C.G.S. units. For instance, the .March, 1902, 

 Declination table is headed D= 151"+ , and the value entered under 1 a.m. of the 2nd is 118' g l. This 

 means a Declination of 151 + 118'-!, or 152 58' g l, at the hour stated. Owing to the large size of the 

 daily range of Declination, it was impossible to avoid entries exceeding 60'. 



The last four columns give the absolutely highest and lowest values of the element shown on the day's 

 trace, and the time or times of their occurrence. Thus on .March 2, 1902, the absolutely largest or 

 maximum reading on the Declination trace was 151 + 179'-6, i.e. 153 59'"6, and its hour of occurrence 

 was 6h. 7m. in the morning, local time. 



In the case of the Vertical Force, information as to maxima and minima is confined to days when the 

 photographic record was complete except for the interval occupied in changing the papers. 



In general the cause of absence of hourly readings is indicated in the tables, the letters n, a', //, <; </, being 

 employed for brevity with the following meanings : 



a no trace of the element, usually from no paper being on the drum ; 



a,' (in case of Vertical Force) no temperature trace ; 



b (special case of a) a gap between successive sheets which could not be filled in satisfactorily 



c trace existent, but either too faint or too confused to tabulate ; 



'/ instrument recording, but not working satisfactorily. 



When the magnetograph in question was working, but the trace was beyond the limits of registration, 

 the fact is indicated by inserting the value answering to the extreme limit of registration, followed by a 

 plus or a minus sign according to circumstances. For instance, in December, 1902, the Declination is <<iven 

 in the table as (150 + ) 326''0+ at 6.5 a.m. on the 2nd, and as (150 + ) 30''5 - at 8.10 a.m. on the 10th. 

 This means that on the former occasion the Declination was beyond the limit (150 + ) 326' - of possible 

 registration in the direction of high Declination, while on the latter occasion it was beyond the limit 

 (150 + ) 30'-5 of possible registration in the direction of low Declination. This explanation applies both 

 to maxima and minima and to hourly values. 



In the case of Declination and Vertical Force the trace was registered right up to either edge of the 

 sheet. In the case, however, of Horizontal Force the light from the lamp began to be eclipsed whilst the 

 trace was still considerably short of that edge of the sheet which answered to low values of the force, 

 and the trace became fainter and fainter, eventually vanishing at a distance from the edge which varied 

 sensibly with the brightness of the lamp and the development of the photographic paper. 



The most usual time to change papers was within an hour or two of noon, so that a day's trace 

 appeared usually on two different sheets (sometimes on more, when there were quick runs). 



In the case of the Vertical Force there was the complication that the edge of the sheet had a constantly 

 varying value unless temperature were absolutely steady. When Declination or Horizontal Force was 

 highly disturbed, the trace might be repeatedly off and on in the course of an hour. The most 

 appropriate entry in these cases was only decided after investigation of the special features. That absolute 

 consistency prevailed in the treatment is hardly likely, but uniformity was aimed at, so far as possible 

 (w Chap. III). 



