132 



REPORT ON 



(m -J- L) was positive. Things being thus arranged, a weight was placed on the 

 paper scale to prevent it from moving. Then a ruler being laid so that, while it 

 crossed the line erf at a distance from a equal to b', it also crossed the line e/at a 

 distance from b equal to 5" (the distances 6' and 5" being taken above the line ab 

 if they were positive, beloio it if they were negative), the reading of the point on the 

 paper scale where the ruler crossed its edge was the required value of $. In that 

 way, without again moving the paper scale, the values of the deviations on each 

 of the thirty-two true magnetic points were computed from the observed values. 



The following table contains the constants which were used in computing from 

 the observed deviations the deviations on the true magnetic points. The first 

 column gives the name of the station. The second column, the distance in miles 

 from the ship to the object used as an azimuth mark. The third column, the 

 assumed magnetic azimuth of the object used as an azimuth mark; the azimuth 

 being counted from the south around by the west. The fourth column, the true 

 magnetic azimuth of the same object, found by applying the magnetic declination 

 given in the table on page 61, section IV, to the true azimuth given in the table 

 on page 36, section III. The fifth column, the value of m. The sixth column, 

 the value of L; and the seventh column, the value of (m -\- L). 



The following tables contain all the deviations of the compasses which were 

 observed during the cruise. In each table the first column contains the assumed 

 magnetic azimuth of the ship's head at the time the reading of the compass, given 

 on the same line in the second column, was taken. The third column contains the 

 observed deviation of the compass for each point, obtained by subtracting the 

 readings in the second column from those in the first column. Hence, a deviation 

 of the north point of the compass to the cast is designated by the sign -|- ; a 

 deviation to the west by the sign . The fourth column contains the deviation 

 of the compass on each of the thirty-two true magnetic points, obtained from the 

 observed deviations in the manner already explained. 



