Work in the Pacific Ocean 



6ii 



as possible of the iron in tlie blocks and 

 tackle by non-magnetic metal, and the 

 building of a special observing bridge, 

 running fore and aft between the masts 

 and placed about 15 feet above the deck. 

 The instruments mounted on this bridge 

 were, on the average, about 25 to 30 feet 

 from the remaining masses of iron, con- 

 sisting chiefly of the iron bolts in the sides 

 of the vessel. 



^^'hile, then, it was not possible to con- 

 vert the Galilee completely into a non- 

 magnetic vessel, as would have been de- 

 sirable, the changes made resulted in 

 reducing the corrections due to the dis- 

 turbing influences of the iron to such an 

 extent that the so-called "ship's magnetic 

 constants" turned out to be smaller for 

 this vessel, on the average, than those of 

 any vessel thus far engaged in oceanic 

 magnetic work. 



However, the corrections are still large 

 enough so that they require to be taken 

 into account to satisfy the requirements 

 of the work. These corrections must be 

 determined by special observations, con- 

 sisting of swinging ship in port and at 

 sea as often as circumstances will permit, 

 which necessarily cause more or less de- 

 lay in both the field and office work. Un- 

 fortunately, experience during the past 

 two years has also repeatedly shown that 

 these corrections do not strictly follow the 

 physical laws prescribed by the analysis 

 of the deviations, namely, the corrections 

 arise chiefly from the magnetic induction 

 in the soft-iron parts of the vessel, and 

 hence are subject to various accidental 

 conditions, such as length of time pur- 

 sued by the vessel along any one course 

 or the amount of buffeting the vessel has 

 been exposed to from the waves, etc. 



It would be more economical all around 

 were it possible to secure an entirelv 

 non-magnetic specially built vessel. The 

 construction of such a vessel presents no 

 mechanically unsurmountable difficulties. 

 It seems a pity that in the very regions 

 where the disturbances due to local mag- 



netic masses are a minimum we should 

 introduce an extraneous source of dis- 

 turbance by not having an entirely non- 

 magnetic vessel. 



It is hoped that the necessary funds — 

 about $75,000 — may soon be secured for 

 the construction of a vessel suited to the 

 importance of the work undertaken. The 

 new vessel would be again a wooden sail- 

 ing vessel, built somewhat along the same 

 lines as the one at present employed, ex- 

 cept that no material whatsoever having 

 a magnetic influence would be used. This 

 would mean the exclusion of all iron and 

 steel except such as would come at a dis- 

 tance far enough awa}' as not to affect the 

 magnetic instruments. 



An all-sailing vessel, however, does not 

 permit the magnetic survey to be under- 

 taken with the completeness and success 

 demanded, since with such a vessel it is 

 more or less dangerous to investigate the 

 magnetic irregularities almost invariably 

 shown to exist near land masses. The 

 mapping of these irregularities is of the 

 greatest importance to the mariner, as 

 in many cases they are sufficient, if not 

 allowed for, to land a vessel on the rocks. 

 For such close shore-work it is essential 

 that the surveying vessel be provided 

 with some auxiliary motive power in ad- 

 dition to that derived from the sails. 

 This auxiliary power would be supplied 

 by a gas or gasoline engine, in which but 

 a very small amount of steel is required, 

 the engine being furthermore at such a 

 distance from the instruments as not to 

 have an effect. 



Besides greatly facilitating the ac- 

 Cjuirement of the magnetic data and re- 

 ducing the running expenses, the new 

 vessel would materially add to the safety 

 and comfort of those on board who are 

 devoting their lives to such arduous 

 work. Let us therefore hope that the day 

 is not distant when the magnetic survey 

 of the oceans can be undertaken with 

 the completeness, the expedition, and 

 safety that its importance demands ! 



