Instructions for the Galilee Work 117 



degreeof accuracy in the determination of the magnetic elements may be obtained. * * * Certain 

 observations on August 7 show very clearly that, between the inclination and the intensity obser- 

 vations, something occurred which caused a different distribution of iron masses within the region of 

 influence. * * * 



3. It is also extremely essential that the observer remove from his person all articles likely to 

 affect the instruments, and it would be well to devise some form of statement to be entered in the 

 report of the observations to insure that this has been done. * * * 



From Directions of October 16, 1905, to J. F. Pratt, Honolulu. 



1. On the 12th instant, the following cablegram was sent you to Honolulu: "Daily swings 

 necessary. Instrumental changes require closing San Diego instead San Francisco. Instead failing 

 deflections observe usual dips. Acknowledge." * * * 



2. We are having great difficulty, for one reason or another, making the deviations fit theory, and 

 it is believed that the only safe course to follow is to svnng every day,' so that the mean results will 

 be free from uncertainty on account of deviation. It will be a great saving, especially in the compu- 

 tation, if we do not have to bother with deviations. With this experience in mind, please do your 

 utmost to secure swings as often as possible. * * * 



3. You will doubtless swing the Galilee off the coast near the Honolulu Magnetic Observatory, 

 about where you s^vung the Patterson, of the Coast and Geodetic Survey, in 1904. The cablegram 

 calls for dip observations in place of the deflections when they fail. * * * 



From Directions of October 17, 1905, To J. F. Pratt, Honolulu. 



1. Before it is possible to reduce completely the observations from San Diego to Honolulu, it 

 will be necessary to secure some good swings at Honolulu at the place mentioned in the letter of 

 yesterday. At least two good swings are desired: for example, one a. m. and one p. m., to be re- 

 peated, if observations are not satisfactory. The inclination and intensity observations should 

 be made thus: a. m., observations with loaded needle on first helm, next inclination observations 

 with needle No. 1, say on the other helm swing; p. m., observations with loaded needle on helm 

 opposite that of the morning; next inclination observations with needle No. 1 (polarities reversed) 

 on other helm. It would be preferable if observations could be made on each heading for each of 

 the positions of the circle (both for the loaded needle and the dip needle). Thus, the observations 

 on each heading would be for the positions: face circle east; face needle east; face circle west; face 

 needle west; etc. 



2. Swings with dip needle and loaded needle should be kept up after leaving Honolulu until the 

 deflection method becomes available again with the sea dip-circle, after which it will be desirable to 

 alternate ; for example, on one day swings with loaded needle and with dip needle, while on the next 

 day, swings will be made with the loaded needle, followed by deflections. 



3. At San Diego, the port of arrival, swings will be made, using both methods given in 2. 



4. Inclination observations at the land station should hereafter be made regularly by the 

 direct method, also with needle 3, not reversing polarities, however, in the latter case. It will 

 therefore be necessary, before you leave Honolulu, to make such observations at the Honolulu 

 Observatory in sufficient number to give a good value of the correction required to reduce the 

 inclination thus obtained with No. 3 to the standard value. Whenever the deflection method 

 is applicable, the inclination will likewise be obtained in this way, in order that the data may 

 be derived for determining the corrections on account of non-reversal of polarity of deflected 

 needle. * * * 



From Instructions of November 22, 1905, to J. F. Pratt, San Diego, Cal. 



1. In addition to the directions contained in the instructions of August 15, and letters of 

 September 18 and October 16 and 17, respecting the closing work at San Diego, complete magnetic 

 observations (Z), H, I) at both C. I. W. shore stations Nos. I and III, between which the ship was 

 swung last August, are to be made. At both of these stations, furthermore, standardization ob- 

 servations will be made with the dip circles, and the intensity constants will be determined for the 

 sea dip-circle, and for the sea deflector. 



'Owing to meteorological conditions encountered, this did not prove feaaible. 



