210 Ocean Magnetic Observations, 1905-10 



CRUISE IV. MARCH 1915 TO SEPTEMBER 1916. 

 Magnetic Instruments. 



XXXIV. For magnetic declination at sea. (!) Marine collimating-compass 1, same as 

 for Cruise III; (2) sea deflector 4,' same as for Cruise III. The designations adopted, 

 respectively, for the two compasses with appurtenances axe CI and D4. (3) Sea deflector 5, 

 provided with deflecting magnet 5, designed and constructed by the Department of Terres- 

 trial Magnetism, from April 1916, for reserve and experimental use; (4) Ritchie liquid 

 compass 29971, same as for Cruise III; (5) Ritchie hquid compass 29499, and (6) Ritchie 

 Hquid compass 29497, same as for Cruise III; (7) Ritchie Uquid compass 39670, same as 

 for Cruise III; (8) sea deflector 3 was on board from June 1915 for possible emergency use. 



XXXV. For magnetic inclination and total intensity at sea. (1) Sea dip-circle 189, 

 same as for Cruise III, with dip needles 1, 2, 5, and 6, and mtensity-needle pairs 3 and 4, 

 and 11 and 12; (2) sea dip-cucle 204, provided with dip needles 2, 9, 10, and 11, and inten- 

 sity-needle pairs 3 and 4, and 7 and 8;^^ (3) marine earth-inductor 3, same as for Cruise III 

 with the addition, for use at shore stations, of galvanometer 28A and tripod, designed and 

 constructed by the Department of Terrestrial Magnetism. The designations adopted, 

 respectively, forthe three instruments and their appurtenances are 189.125634, 204.2934, and 

 EI3. For the dip circles the intensity-needle numbers are itaUcized; for cases where both 

 deflection and loaded-dip observations were made, the designation for the intensity needles 

 is followed by a dagger (f), thus, 189.12,n,/;2t- 



XXXVI. For horizontal intensity at sea. (1) Sea deflector 4, same as for Cruise III. 

 The designation adopted for the deflector is D4. (2) Sea deflector 5 with deflectmg mag- 

 net 5 was on board from AprU 1916, as a reserve instrument; (3) sea deflector 3 was on 

 board from June 1915 for possible emergency use. 



XXXVII. For magnetic declination and horizontal intensity on land. (1) TheodoUte 

 magnetometer 5, same as for Cruise III; (2) magnetometer-inductor 25,^ same as for Cruise 

 III. The designations adopted, respectively, for the 2 magnetometers are 5 and 25. 

 (3) Universal magnetometer 21, designed and constructed by the Department of Terrestrial 

 Magnetism, was used at one shore station in March 1915. 



XXXVIII. For magnetic inclination on land. (1) Magnetometer-inductor 25, same 

 as for Cruise III; (2) land dip-chcle 201, provided with dip needles 5 and 6 of 201, 5X, and 

 6X, and intensity-needle pair 3 and 4, with tripod 201, all by A. W. Dover, until May 9, 

 1916. The designations adopted, respectively, for the two mstruments are EI25 and 201.56, 

 5X, 6X. (3) Marme earth-mductor 3 was also used for shore observations; (4) universal 

 magnetometer 21, provided with needles 1 and 3 of 19, and 3 and 4 of 20, was used at one 

 shore station in March 1915. 



Atmospheric-Electric Instruments. 



XXXIX. Instruments for observations in atmospheric electricity. (1) Conductivity 

 apparatus 3, designed and constructed by the Department of Terrestrial Magnetism, pro- 

 vided with gimbal rings and mounting, and direct-current motor; (2) ion counter 1, pro- 

 vided with gimbal rings and mounting, and appurtenances, all designed and constructed 

 by the Department of Terrestrial Magnetism; (3) penetrating-radiation apparatus 1, 

 provided with gimbal rings and mounting, and appurtenances, all designed and constructed 

 by the Department of Terrestrial Magnetism; (4) potential-gradient apparatus 2, complete 

 with appurtenances and mounting, all designed and constructed by the Department of 



'Minor repairs were made during January 1915 on deflector 4 in the instrument shop of the Department of Terrestrial 

 Magnetism. 



^Intensity needles 7 and 8 and dip needle 9 were returned in April 1915, the pivots of 8 and 9 having been broken during 

 observation. 



^Magnetometer inductor 25 was thoroughly overhauled and minor repairs made during January 1915 in the instrument 

 shop of the Department of Terrestrial Magnetism. 



