Discussions of Ocean Magnetic Work, 1905-16 



437 



tory at Cheltenham, Maryland, with an approximate factor applied to those for declination 

 to refer them to Gardiners Bay. 



An inspection of the figures in Table 101 shows, for each year the swing observations 

 were made, that the residuals are small; for D and I, they generally are less than 0?1, and 

 for H, usually less than 0.0005 c.g.s. The residuals are, in fact, on the order of the error of 

 observation. 



Table 101. 



-Residitals from Magnetic Observations on the Carnegie during Swings of Vessel in Gardiners Bay, 



1909-1916. 



[The residuals are expressed in minutes of arc for declination and inclination, and in units of the fourth decimal c.a.a. 

 for horizontal intensity. A phis sign means a deflection of the north-seeking end of the magnetic needle towards the east or 

 downwards; it also signifies an increased value of horizontal intensity.) 



The observations were found to be of such an order of accuracy as to warrant a separa- 

 tion of the results for the port-helm swing and the starboard-helm swing. When this was 

 done, it appeared at first that there was some evidence of small ship-deviation effects. 

 However, when the results were analyzed, it turned out that the effects were to be ascribed 

 to small local disturbances at the place of swing, in Gardiners Bay, of the same nature as 

 those shown by magnetic observations on islands close by. While the vessel was swung 

 around the anchored buoy, she would pass over somewhat different "bottom" or ground, 

 the area of swing being covered by a circle of about 2 or 3 miles diameter, and the average 

 depth of the water being about 6 fathoms. 



The final conclusions were : 



1. That the residuals from the swing observations in Gardiners Bay could be fully 

 explained by errors of observation and by small local irregularities in the Earth's magnetic 

 field within the region of the swings. 



2. That if there are outstanding effects to be ascribed to any magnetic material on the 

 Carnegie, they are of such a subordinate magnitude as not to require being taken into 

 account in the observational, or in the computational work. 



Possibly no further testunony is needed as to the perfection reached in the ocean mag- 

 netic work on the Carnegie than that afforded by Tables 99 and 101. It is seen that, under 

 favorable conditions of sea and weather, it is possible, with the instrumental appliances and 

 methods used on the Carnegie, to make magnetic observations approaching in accuracy those 

 made ashore on fixed supports. 



