DEPARTMENT OE TERRESTRIAL MAGNETISM. 201 



OEFICE WORK. 



On account of the extensive field operations in progress, as narrated above, 

 and owing to the planning, constructing, and equipping of the Carnegie, the 

 time of the office force has been necessarily largely consumed with adminis- 

 trative, executive, and experimental matters. The standardization of the 

 various instrumental outfits, both for sea and land work, with the necessary 

 accuracy, have been made as required. 



The current field observations have been reduced as received, and consider- 

 able progress was made in the preparation for publication of the magnetic 

 results thus far obtained on land and sea. The compilation of past magnetic 

 data and the indexing of current literature have been continued, and ab- 

 stracts of publications of special interest have been prepared from time to 

 time. Letters of information and data have been supplied in response to 

 inquiries. 



STANDARDIZATION OE DIP INSTRUMENTS. 



A discussion of the results obtained by the Galilee in the Pacific Ocean 

 revealed the desirability of being able to examine at Washington a dip instru- 

 ment within the entire range of dips likely to be observed. Thus in the 

 Pacific Ocean this range was from +75° to — 60°. For such a large range it 

 is an interesting as well as a practical question to find out how the correction 

 required to reduce the results obtained to an absolute standard will vary 

 with dip. 



Accordingly a special apparatus was devised by Mr. P. H. Dike, by which,, 

 with suitable electric coils, it was possible to create the desired artificial field 

 to produce the dip sought. A description and a first communication of the 

 results obtained from the comparisons of the earth inductor with land and 

 ship dip circles under such conditions was published by Mr. Dike in the issue 

 of the journal "Terrestrial Magnetism" for September, 1909. The apparatus 

 promises to be a useful adjunct in the study and elimination of the causes of 

 errors of magnetic instruments. 



CONSTRUCTION OE INSTRUMENTS. 



The value of having a good instrument shop ready at hand has been amply 

 demonstrated during the past year. There have been constructed a number 

 of specially designed instruments for use on board the Carnegie. First 

 among these is the collimating marine compass No. i, after the design devel- 

 oped chiefly by Mr. Peters. With this instrument a greater accuracy has 

 been obtained in the determination of declination at sea than heretofore, the 

 observations showing an absolute accuracy under favorable conditions of 

 about 0.05°. As a part of this instrument, a small hand circle of reflection 

 has been specially designed and constructed. Both of these instruments will 

 be found described in some detail in the journal "Terrestrial Magnetism" for 

 March, 1909. 



