28 Ocean Magnetic Observations, 1905-16 



18 inches of the foremast. This made possible the arrangement and spacing of the 4 instru- 

 ments (sea dip-circle, standard Ritchie liquid compass, sea deflector, and Kelvin compass) 

 used for Cruises II and III. (See Fig. 1, Plan C.) The inventory of instruments (pp. 

 29-32) will show what particular instrument of each type was in use during the various 

 portions of these cruises. For view of observing-bridge, see Plate 2, Figure 1. 



LAND MAGNETIC INSTRUMENTS. 



At practically every port visited, as already explained on page 15, the ship magnetic 

 instruments were compared with a magnetometer and a land dip-circle or an earth inductor. 

 Before and after each cruise, or whenever returned to the Office, the land instruments 

 carried by the vessel were always standardized at Washington by direct comparisons with 

 the standards adopted for the reduction of all results to a common basis ; those standards, 

 designated as "C. I. W. Standards" (see p. 77), are the same as given in Volumes I 

 (p. 42) and II (p. 16). In order to supplement the direct comparisons and to control any 

 possible changes in the constants, additional checks were secured, whenever opportunity 

 offered at ports visited, by comparisons with reserve land instruments carried by the vessel, 

 or with instruments in use by observers of the Department of Terrestrial Magnetism engaged 

 in other field work. The specific land and ship instruments will be found mentioned in the 

 inventory on pages 28-32. The types of land instruments used are fully described and 

 illustrated in Volumes I (pp. 2-11) and II (pp. 5-15) ; the types of ship instruments used are 

 described and illustrated on pages 17-26. 



INSTRUMENTAL OUTFIT FOR THE GALILEE WORK. 



CRUISE I. AUGUST TO DECEMBER 1905. 



Magnetic Instruments. 



I. For magnetic declination at sea. — (1) Ritchie liquid compass 29971, provided with 

 azimuth circle 387-III and brass binnacle 316 for use on board ship and tripod for use on 

 shore, all by E. S. Ritchie and Sons; (2) Negus liquid compass 31974 (manufactured by 

 E. S. Ritchie and Sons), provided with a Negus azimuth circle and a wooden binnacle for use 

 on board ship (the tripod for 29971 was used for shore work with 31974) ; (3) Kelvin dry 

 compass (card 20, Pat. 8050) and bowl (13, Pat. 5892), provided with extra card (Pat. 

 15625), extra pivot and bearing, and Kelvin azimuth instrument 3619, by the Kelvin and 

 James White Company, mounted on board ship in a wooden binnacle suppHed by T. S. 

 and J. D. Negus. The designations adopted, respectively, for the 3 compasses with their 

 appurtenances are: RIA, Dl, and K. 



II. For magnetic inclination and total intensity at sea. — Sea dip-circle 169, with dip 

 needles 1 and 2 and intensity needles 3 and 4, provided with brass gimbal-stand 169 for use 

 on board ship and tripod for use on shore, all by A. W. Dover. The designation adopted 

 for the dip circle is 169, followed by the numbers of dip needles in Roman type and of inten- 

 sity needles in itahcized type, thus: 169.12, 169.134, 169.34, etc. For cases when the 

 intensity results are from both deflection and loaded-dip observations the designation 

 of the intensity needles is followed by a dagger (f), thus: 169.34t- 



III. For horizontal intensity at sea. — Sea deflector 1, designed and constructed by the 

 Department of Terrestrial Magnetism, consisting of special attaclmients and mountings 

 for the Negus azimuth circle used on Negus liquid compass 31974 and provided with deflect- 

 ing magnets 45 and NL. The designation adopted for the deflector and compass is Dl. 



IV. For magnetic declination and horizontal intensity on land. — Magnetometer 36, 

 complete with tripod, deflection bar, and appurtenances, by T. Cooke and Sons, and sup- 

 plemented with theodolite 5464 and tripod for astronomical observations on shore, all 



