56 



Ocean Magnetic Observations, 1905-16 



weight 1 for sea deflector, D2, because the deviation-corrections were much more strongly 

 determined for the former instrument. 



As seen from Table 3, page 55, the 4 sets of p. m. observations, with instrumental 

 corrections applied, were +9?05 and -t-9?23, respectively, for standard compass and sea 

 deflector. Since the course was again WSW, the deviation-corrections were the same as for 

 the a. m. observations, viz: — 0?08 and — 0?21 respectively. The final results were 8?97 E 

 for the standard compass (R3C) and 9?02 E for the sea deflector (D2), the weighted mean 

 being 8?99 E, or 8° 59' E (latitude 5° 41' S; longitude, 99° 55' W). For explanation of 

 instrumental corrections see page 62. 



It will be observed that whereas the range in the corrected values of the declination 

 (see last column of tables), is about 1° for the a. m. observations when the vessel was rolling 

 from side to side 30° and more, it is but 0?3 for the p. m. observations, although the roll of 

 the vessel was 20°. When it is considered that a single value of the eight a. m. or p. m. 

 sets depends upon observations made during an interval of time of about one minute, the 

 results, under the conditions encountered, must be regarded as very satisfactory. 



The horizontal-intensity observations with sea deflector 2 (D2), given on page 49 

 are presented in detail for two of the four sets, with each magnet 2L and 45, but for 

 the other sets only the mean results are given in Table 4, viz, the two sets below the 

 detailed results for each magnet. These observations were computed on Form 25, as 

 shown on page 38, using the final value of log mC as given on page 64. The value of H 

 resulting from the computation was 0.3282, which became 0.3304, when the deviation- 

 correction -t-0.0022, page 92, was applied. The results in detail are shown in Table 4. 



Table 4. — Valxtes of Horizontal Intensity with Sea Deflector 2, on April 14, 190S, P. M. 

 (Latitude, 5° 41' S; longitude, 99° 65' W.) 



The total-intensity observations given on pages 50-52 were computed on Form 25a, 

 as explained on pages 42-43. Final values of log Ca and log C,, given in Table 18, page 70, 

 were used in making this computation. The final results for long and short distances were 

 respectively: 0.3270 and 0.3266, the mean giving 0.3268 for the horizontal intensity by 

 deflections, while 0.3267 was the result by the loaded needle. In this case the deviation- 

 corrections were -f 0.0026 and +0.0008, respectively, giving the final values of 0.3294 by 

 deflections and 0.3275 by loaded needle. The final weighted mean of the three values of 

 the horizontal intensity, 0.3304 by deflector, weight 3, 0.3294 by dip-circle deflections, 

 weight 2, and 0.3275 by dip-cu-cle loaded needle, weight 1, was 0.3296 (latitude, 5°41'S; 

 longitude, 99° 55' W), as given in the Table of Results (p. 104). 



The satisfactory accord in the three values of H shows how completely successful 

 were the attempts to make the sea dip-circle available for total-intensity observations, even 

 in the lowest magnetic latitudes, and to devise as well an instrument, the sea deflector, 

 for measuring directly horizontal intensity. 



