Reduction Formul-^c and Instrumental Constant.? 



Table 52. — Constants 0/ Marine CoUimating-Compass CI. 



235 



'The magnetic azimuths are on the basis of C. I. W. Standard and are reckoned continuously in a clockwise direction 

 from the magnetic south as 0° through 360°. 



'Elevations above the horizon are reckoned as positive, and below the horizon as negative. 



"The vertical intensity, Z, is expressed in c. a. s. units, and is reckoned as positive for the northern magnetic hemisphere 

 and negative for the southern magnetic hemisphere. 



Table 53. — Periodic Corrections to Card Readings of Compass D3. 



Table oi.— Corrections to Observed Card-Readings of Compass D3 by the "Bright-Line" Method. 



The cause of the change in the index error, early in October 1910, at Pmheiro, is not 

 known. 



Sea deflector 4 (D^).— Sea deflector 4 was used on Cruise II, beginning at Cape Town 

 in April 1911. The instrument was taken apart at Batavia, Java, in October 1911, to 

 refasten one of the compass magnets which had become loose; it was again taken apart 

 at Longwood, St. Helena, in June 1913, to remove an air bubble. The adjustments were 

 altered somewhat at each reassembling of the instrument. There are no periodic correc- 

 tions to observed card-readings of the compass D4. The "shadow" method was not used 

 on Cruise II; however, it was used occasionally on Cruise III. The adopted corrections, 



