MAGNETIC OBSERVATIONS 291 



20 to April 1 6, 1904 : 



= 22 43/7 + 27/93 sin (6 + o 26') + 7/96 sin (2 + 274 24') + 

 2/67 sin (3 e + 149 03') + 3/56 sin (4 e + 65 34') 0/39 



April 17 to May 14, 1904 : 



D = 22 37/1 + 25/51 sin (e + 353 22') + 8/81 sin (2 9 + 287 10') + 

 3/37 sin (3 + 224 52') + 3/81 sin (4 * + 24 14') 0/27 



May 15 to June n, 1904 : 



D=22 40/1 +3o/3i_ sin (# + 350 15') +9/14 sin (20 + 308 51') + 

 6/64 sin (3 0+~223 42') + 1/50 sin (40 + 31 56') 0/39 



June 12 to July i, 1904: 



D=22 32/1 +41/83 sin (0 + 341 19') + 8/65 sin (2 0+ 309 04') + 

 4/57 sin (3 * + 1 56 34') + 3-'8 sin (4 + 100 30') 0/53 



For whole observational series, October 4, 1903, to July i, 1904 : 



D=22 42/0+20/52 sin (0 + 357 14') +7/69 sin (20 + 294 16') + 

 1/50 sin (30+177 59') + i -'Si sin (40 + 47 52')o/i2 



For the year, July i, 1903, to June 30, 1904, from monthly grouping of observations and 

 interpolations therefrom : 



D = 22 38/5 + 21/11 sin (0 + 354 18') +6/90 sin (20+291 26') + 

 1/75 sin (3 0+156 48') + 1/62 sin (4 + 58 51') 0/20 



Month of July, 1903 (interpolated values) : 



D = 22 24/9 + 32/62 sin (0 + 341 59') + 5/95 sin (2 + 291 36') + 

 4/79 sin (3 0+154 3<>') + 2/73 sin (4 + 84 45') 0/75 



Month of August, 1903 (interpolated values) : 



D=22 25/8 + 24/66 sin (0 + 343 19') + 4/26 sin (20+ 273 14') + 

 3/59 sin (30+116 51') + 2/63 sin (40 + 86 04') 0/90 



Month of September, 1903 (interpolated values) : 



D=22 30/9+17/95 sin (0 + 351 52') + 5/09 sin (20+272 49') + 

 2/25 sin (30 + 72 56') + 2/28 sin (40 + 90 30') 0/66 



In all of these expressions the angle counts from 15 as 0.5 hour A. M. local mean time. 

 The formulae have been carried to terms of the fourth order only, as little or no improvement 

 results from the further extension of the function. Graphical representations to scale of these 

 formulae, together with the quantities from which they are deduced, are given by figures 5 to 19. 



A comparison of the diurnal variations represented by the four sine terms of the analyt- 

 ical expressions with the observed quantities at the mean local half hours, is given by the 

 following tabulation wherein the observed, interpolated, and computed values on mean of day 

 are indicated by the letters O, /, and C respectively. As a criterion of the accuracy of the 

 formulae for diurnal variation, a column showing differences of observed and computed varia- 

 tions is added ((O-C) or (7-Q). In these tabulations a plus sign indicates the variation to 

 be to the east of mean declination for day, while a minus sign indicates the variation to be to 

 the west of mean declination for day. The extreme values on the half hours for each period, 

 both observed and computed, are indicated by bold-face type. 



