THE 



VOYAGE OF H.M.S. CHALLENGEB. 



I. M EMORANDUM on the MAGNETICAL OBSERVATIONS made during 

 the Voyage of H.M.S. Challenger, 1872-76, prepared in the 

 HYDROGRAPHICAL DEPARTMENT of the ADMIRALTY, under the Superin- 

 tendence of the HYDROGRAPHER. 



When at the request of the Royal Society the Government decided upon sending 

 H.M.S. Challenger upon her recent voyage of scientific research, the subject of Ter- 

 restrial Magnetism was amongst others brought forward as one of importance, both 

 in the interests of science and safe navigation. Preparations were accordingly made 

 for as complete a magnetic survey of the ports visited and seas traversed, as time and 

 circumstances would permit. 



The necessary equipment of magnetical instruments, and the preparation of instruc- 

 tions for the officers to be engaged on the service were placed in the hands of Captain 

 F. J. Evans, R.N., F.R.S., then in charge of the Admiralty Magnetical Department. 



A list of the instruments furnished originally to the " Challenger " is given in the 

 " Magnetical Instructions," a copy of which is appended. A third Fox Dip and Intensity 

 apparatus was sent to the ship at St Vincent (Cape de Verde islands). Of these instru- 

 ments the Unifilar Magnetometer, the Barrow's Dip Circle, and the Fox apparatus were 

 examined at Kew, and their several constants determined by the officials of the 

 Observatory. 



The officers selected to conduct the observations (under Captain Nares) were 

 Commander Maclear and Sub-Lieutenant Sloggett. These officers were instructed in 

 the use of the various instruments at the Hydrographic Department of the Admiralty 

 and at Kew Observatory. Sub-Lieutenant Sloggett was obliged by ill health to leave the 

 ship at Halifax in May, 1873, his place being then taken by Lieutenant Bromley. 

 - VOL. ii. A 



