216 



SCIENCE. 



[Vol. IX., No. 213 



of the sextant, and comparisons of chronometers 

 were made throughout the stay of the party. 

 From a series of observations of double altitudes 

 of the sun (near lower transit), and of circum-meri- 

 dian altitudes of the sun (upper transit), the latitude 

 was found to be SI'' 44' 00." 4 ± 5.''4. The azimuth 

 of the mark for absolute declination was deter- 

 mined on three days from observations of the sun 

 with a theodolite, viz., 44'=' 44'.3 ± 0'.8 east of 

 south. The longitude of the station from Green- 

 wich was determined by means of ships" chro- 

 nometers on the outward trip, and at the station 

 by observations of moon culminations, occulta- 

 tions, and lunar distances, with the result ^ 18™ 

 538.3 ± 18.2 west of Greenwich. 



The accuracy of this result is mainly due to a 

 fine series of seventeen moon-culminations. In 

 arc, the longitude is 64'' 43' 50" W., and the value 

 preliminarily adopted by Lieutenant Greely for the 

 use of his party was 64^* 45' W., on the autht)rity 

 of Lieutenant Archer, E.N., as the result by the 

 British expedition to this place in 1875-76. 



During the first ten months of the occupation of 

 the post a series of hourly observations of the dec- 

 lination were made on three days in each month : 

 this comprises the period from Aug. 1, 1882, to 

 Aug. 31, 1883, and includes 846 observations, with 

 a resulting declination lOO'* 13'.6 west of north. 

 The results of the diurnal variation of the declina- 

 tion are stated as follows : on the yearly average 

 the needle reached its extreme westerly deflection 

 between ^^ and ^ p.m. (local time), amount 45', 

 and its extreme easterly deflection between (fi^ and 

 21* A.M. (local time), amount 40', hence the diurnal 

 range 1° 25'. The diurnal variation is illustrated 

 by a diagram. 



The series of hourly observations of the declina- 

 tion at Fort Conger began with July 1, 1882 and 

 ended with Aug. 1, 1883 ; this is the period which 

 was assigned by the international commission to 

 be that of close and simultaneous co-operative 

 magnetic work obligatory on all parties. The 

 differential measures of this series were converted 

 into absolute values : the tabulation and discussion 

 of this series constituted the greater part of the 

 labor expended on the observations. The method 

 of separating the so-called disturbances from the 

 general record, and their treatment when sep- 

 arated, was left, apparently, by the Vienna con- 

 ference to the discretion of each individual party, 

 though several methods were proposed. It is well 

 known that there is no certain criterion of what 

 constitutes a disturbance, and, moreover, pro- 

 cesses that may answer in lower latitudes will be 

 found difficult of application for stations in high 

 magnetic latitudes. It would take too much space 

 to explain here this rather technical subject : it 



may be sufficiently described, however, by stating 

 that the mean deviation of an observed value from 

 its respective hourly and monthly normal value 

 was first made out. Then, according to Dr. 

 Lloyd's rule, one and a half times this value, or, 

 in the case of Fort Conger, 1° 06' was considered 

 the limiting value, and any observation differing 

 by this or a greater amount from the normal value 

 was designated 'a distui'bance.' 



These hourly normals and (larger) disturbances 

 were tabulated and the results were discussed. 

 The average declination from this series is 100° 

 34'. 5 W., and when compared with the earlier re- 

 sult of the British expedition gives 9'. 9 as the 

 most probable value for the annual diminution of 

 west declination at this place. It is shown that 

 the effect of the presence of these (larger) distur- 

 bances was to diminish the declination by 2'.3, 

 and that the diurnal range of the motion of the 

 needle was increased by their influence. 



The solar-diurnal variation of the declination is 

 presented in tabular and analytical form as well as 

 by a diagram : its most characteristic feature is 

 the occurrence of the westerly extreme soon after 

 local noon, with a deflection of 37'. 9, reached 

 earlier in summer and later in winter. The oppo- 

 site extreme is reached an hour and a half after 

 midnight, with a deflection of 27'. 9, also found 

 variable with the season. Average dmrnal range, 

 October to March, 0" 56', and April to September, 

 I'' 22'. In the annual variation of this average 

 range. December exhibits the minimum of 28', 

 and June the maximum of 1^ 48'. The lowest 

 reading on record was on Nov. 16, 1882, at 8^1 35™ 

 A.M. (Gottingen time), when the declination was 

 92° 5 1'. 6 W., and the highest reading on the day 

 following at 10^^ 20™ p.m. (Greenwich time), viz., 

 113° 19'.8 W., showing a change of no less than 

 20'=' 28'. 2 within thirty-eight hours ; and it is noted 

 that a great magnetic storm was raging between 

 Nov. 13 and Nov. 19, 1882, which culminated in 

 intensity on the 17th. 



The total number of hourly observations during 

 the year was 8,749, and the number of (larger) 

 disturbances separated from them, 1,169 ; in other 

 words, there was one (largely) disturbed observa- 

 tion in every eight. 



The distribution of the disturbances in the 

 diurnal and annual periods, with separation into 

 easterly and westerly disturbances, was then 

 analyzed and the results were tabulated, with 

 respect to both frequency and magnitude. But 

 for want of space we cannot follow out all the re- 

 sults presented. We may. however, mention the 

 following : during the year (ending Aug. 1, 1883), 

 the easterly disturbances exceeded in number the 

 westerly ones in the proportion of 661 to 508, or 



