176 Ocean Magnetic Observations, 1905-16 



nately, Point Reyes was sighted at 1 o'clock in the morning before the fog closed down. 

 Creeping through the fog until the light vessel was heard, a pilot was taken aboard, and the 

 Carnegie made the entrance into the harbor through the fog under her own power. The 

 total distance nm from Guam was 5,937 miles, the time of passage being 46 days, and the 

 average daily run 129 miles. The chronometers were found in error only 8=7. 



The total distance covered on Cruise IV, from March 6, 1915, to September 21, 1916, 

 was 48,626 miles; as the time actually at sea was 375 days, the average day's run was 130 

 miles. During this period the Carnegie reached the extreme latitudes of 59° 33' N. and 

 60° 33' S. For further infonnation regarding this cruise, see abstract of log, pages 350-356. 



As heretofore, the Carnegie's staff is indebted for special courtesies shown at the ports 

 visited and for valuable assistance rendered by various persons and officials. 



METHODS OF WORK ON THE CARNEGIE. 



The methods adopted and the principles followed were, in general, the same for 

 the scientific work aboard the Carnegie as for the Galilee (pp. 14-16). The chief 

 modifications arose from the fact that the Carnegie is a non-magnetic ship and from 

 the introduction of certain new and improved instruments. 



The Carnegie was designed with the view of making it possible to place the 

 various instruments in the most advantageous positions possible, and far enough 

 apart so that the fundamental principle to have each magnetic element determined 

 independently by simultaneous observations with two different instruments, and 

 by different observers, could be carried out successfully. The actual positions of 

 the instruments may be seen from Figure 13, page 202, and Plate 9, Figure 2. 



To test the question whether at any of the instrument positions there were 

 magnetic effects attributable to anything aboard the Carnegie, the vessel was swung 

 occasionally both in harbor and at sea, and magnetic observations were made on 

 the various headings, as in the case of a magnetic ship like the Galilee. The results 

 of these observations will be found tabulated and discussed in the special report 

 (pp. 423 et seq.). It will be seen that the conclusion as to the absence of any 

 deviation-corrections large enough to be taken in account is well supported. 



There being no troublesome and time-consuming deviation-corrections to 

 determine, the computations and derivation of magnetic data were greatly simplified. 

 The observers reduced their observations and obtained preliminary results of 

 sufficient accuracy for mariners' purposes within an hour after the completion of 

 the observations aboard. Reaching a port, the commander of vessel transmitted 

 an abstract of these results to the Office at Washington, where they were mani- 

 folded and promptly transmitted to the chief hydrographic establishments. There 

 are letters on file from some of these establishments to the effect that they were 

 receiving magnetic data from the Carnegie more promptly than they could be 

 obtained from their own vessels. 



The observation forms were adapted to the new instruments and were modified 

 as experience from time to time suggested. Specimen observations and computa- 

 tions will be found on pages 212-231, also on pages 234, 240, and 243-250. 



In order not to expand the present volume unduly, various matters of interest 

 pertaining to methods of observation and to instrumental appliances must be 

 passed over here and treated in a subsequent volume. 



