436 Reports on Special Researches 



belonging to the various magnetic and electric instruments for work at sea and on shore, 

 and, furthermore, the steel and iron tools required by the engineer and the mechanician. 

 These magnetic materials were also stored aft; the general store room for the magnetic 

 insti-uments and the storeroom for the tools are shown in Figure 9, iniddle plan, page 162. 

 Hence, in the aggregate, there might be considerable magnetic material at any one time in 

 the after part of the vessel. While, according to calculation, it did not seem possible that 

 under any conditions likely to be encountered on probable ciiiises of the Carnegie there would 

 be observable effects from the total mangetic material, it was decided to control this matter 

 observationally. Accordingly, from tune to tune, complete series of magnetic observations 

 were made while the Carnegie was being swung just as though she were a magnetic ship, in 

 fact, observing just as had to be done so frequently in the Galilee work. 



These "swing observations" of the Carnegie were made in Gardiners Bay, usually at 

 the beginning and end of a cruise, at ports where it was known from previous observations 

 there were no pronounced local magnetic disturbances, and occasionally at sea. Possibly 

 in the course of a year there were from 6 to 10 of these special series of observations, the 

 stations varying considerably in magnetic latitude. 



In a later volume there will be brought together the results from all "swing observa- 

 tions" for the various cruises of the Carnegie. It must suffice for the present purpose to 

 give only those derived from the Gardiners-Bay swings, 1909-1915, in latitude 41° 06' 

 north and longitude 72° 13' west of Greenwich. The results for each heading of ship are 

 the means from the observations on the port-helm swing and on the starboard-hehn swing. 

 The details regarding the various swings are as follows: 



1909. The vessel was swung on September 1 and 2, 1909, just before sailing on her first cruise 

 (Cruise I, see pp. 164-165). Owing to inclement weather on the return of the Carnegie in February 

 1910, the "swings" in Gardiners Bay were omitted. 



1910. The Carnegie was swung on June 22, 23 and 25, 1910, at the beginning of the long cu'cum- 

 navigation cruise of 92,829 miles (Cruise II, see pp. 165-170). ^ 



1913. These swing observations were made on December 15 and 16, 1913, after the Carnegie s 



return from Cruise II. 



1914. The Carnegie was swung on October 16, 18, 19 and 20, 1914, after her return from the 

 extreme northerly cruise (Cruise III, see pp. 170-171). 



1915. The swing observations were made on March 7 and 8, 1915, as the Carnegie began the 

 present cruise (Cruise IV, see pp. 172-176). 



The vessel was swung by her own engine or with the aid of a tug. Information 

 regarding the general method of observation followed may be obtained by reference to ex- 

 tracts from Director's instructions (see pp. 317-318). If no interruption occurred because 

 of unfavorable conditions, the total time consumed for a complete swing of 8 headings, 

 with both helms, averaged about 1 hour for declination, and about 3 hours for incUnation 

 and intensity, or about double the tune taken for' the usual magnetic observations at sea. 

 For Cruises I and II, the Carnegie was in command of W. J. Peters, and for Cruises III and 

 IV, J. P. Ault was the commanding officer. Various observers have taken part, the same 

 magnetic element having generally been observed by different individuals and often with 

 different instruments from year to year. 



The residuals given in Table 101 have been obtained by subtractmg the mean value 

 of the observed magnetic element for the 8 headings of the ship, from the values for the 

 individual headings. The plus sign is given the decUnation (D) when east and the incUna- 

 tion (/) when the north-seeking end of the dip needle is below the horizon; the horizontal 

 intensity is always positive. Diurnal-variation corrections were appUed to the observa- 

 tions on the various headings in order to refer all values to the same time. These correc- 

 tions were obtained from the results at the Coast and Geodetic Survey Magnetic Observa- 



