432 Special Reports 



no appreciable difference in the absolute value of inclination for this station; this as- 

 sumption is borne out by the agreement for the differences on the observatory instru- 

 ment resulting from the comparisons with the 2 C. I. W. earth-inductors. The station- 

 differences were determined by the method of simultaneous observations and exchange 

 of stations. 



The standard instrument of the Observatory for declination and horizontal inten- 

 sity is U. S. C. & G. S. magnetometer No. 36, by Cooke and Sons; this instrument is 

 substantially the Magnetic Survey of India pattern. The standard instrument of the 

 Observatory for inclination is Schulze earth-inductor U. S. 0. & G. S. No. 4, of the Wild- 

 Eschenhagen pattern. The corrections applied to observed values to refer these values 

 to the standards of the United States Coast and Geodetic Survey, supplied by Mr. 

 W. W. Merrymon, observer-in-charge at the Observatory, were: for magnetometer No. 

 36 in declination, 0'.4, and in horizontal intensity, O.OOOOOi/; for earth inductor No. 

 4 in inclination, 0'.26. The instruments used by the members of the Carnegie staff 

 were C.I.W. theodolite-magnetometer No. 5, C.I.W. magnetometer-inductor No. 25, 

 and C.I.W. marine earth-inductor No. 3. The finally adopted corrections on I. M.S. 

 have been applied for all C.I.W. instruments. 



The observations were all made as nearly simultaneous as possible. Mr. Merrymon 

 carried out all of the observations with the U. S. C. & G. S. instruments and Messrs. 

 Edmonds and Luke, under the direction of Captain J. P. Ault of the Carnegie, those 

 with the C.I.W. instruments. 



The azimuths used for the declination work were as follows: station Absolute 

 Observatory, north meridian mark of the Observatory about 2,800 feet distant, 180 

 OO'.O, and a telephone-pole about 750 feet distant, 180 24'. 3; station A, north meridian 

 mark of the Observatory, 180 OO'.O, and telephone-pole (same as used for Absolute 

 Observatory), 180 26'.2. The azimuths for the telephone-pole from the 2 stations were 

 determined by angular measurements from the north meridian-mark of the Observatory. 

 At station B the azimuth mark used was a second telephone-pole about 650 feet distant, 

 true bearing of which, from an extended series of Sun observations, was 184 41'. 6. 



Stations A and B are on coral rock, which is easily pulverized by walking about. As 

 a result, there is a great deal of fine dust constantly in the air, and the observers expe- 

 rienced considerable difficulty on this account when working at these 2 stations. This 

 was particularly the case for the observations with the earth inductors, and for this 

 reason the comparisons between earth inductors were limited to the stations Absolute 

 Observatory and A. Another source of trouble at the outside stations was the sudden 

 temperature changes due to passing clouds; variations of as great as 5 Centigrade 

 were noted in intervals as short as 5 minutes. 



Series II, 1921. 



Comparison observations were again obtained during April 15 to 25, 1921, by the 

 Carnegie party. The stations Absolute Observatory and A of 1915 were reoccupied. 

 The standard instruments of the Observatory, their corrections (except for declination) 

 on Coast and Geodetic Survey standards, azimuth marks, and azimuths, were the same 

 as for Series I. The instruments used by the members of the Carnegie staff were as in 

 Series I. The finally adopted corrections on I. M.S. have been applied for all C.I.W. 

 instruments. 



The Director of the United States Coast and Geodetic Survey referring to these 

 comparisons in his letter of August 10, 1921, says: 



"The declination observations with No. 36 appear to have been unreliable for some reason 

 and it has been deemed advisable to use values of declination obtained from the magnetograph, 

 using the mean base-line value. It should be noted that at the time the new observer took charge 



