164 REPORTS O^ INVESTIGATIONS AND PROJECTS. 



the prevalence of local disturbances. In the establishment of a magnetic 

 observatory, however, it might be worth while to consider as a site the 

 vicinity of Mammoth Hot Springs, in the Yellowstone National Park, 

 primarily because of the insured freedom from electric car disturbances. 



Observations under this head embrace, first, the changes in the absolute 

 values of the magnetic elements, with change of level, and, secondly, the 

 changes in the variations (periodic and otherwise) with change of level. 



In the fall of 1903, when the Director was in charge of the magnetic work 

 of the Coast and Geodetic Survey, he investigated the suitability of some of 

 the copper mines in the vicinity of Houghton, Michigan, and found that it 

 would be possible to install instruments at various levels down to 5,000 feet, 

 in chambers from which the ore had been removed, and which were at that 

 time sufficiently distant from extraneous disturbing influences, such as might 

 result from electric installations. Preliminary arrangements were made in 

 cooperation with President McNair, of the Houghton College of Mines, but, 

 being unable to secure promptly from foreign makers the desired instru- 

 ments, the contemplated work could not be carried out. 



The problem of the changes in the magnetic variations with depth is at 

 present being independently investigated also in Germany, under the super- 

 vision of Prof. Adolf Schmidt, in charge of the Potsdam Magnetic Observa- 

 tory, a preliminary account of which has been published in the December, 

 1906, issue of the journal Terrestrial Magnetism. 



SPECIAL OBSERVATIONAL WORK. 



Besides the various observations required at Washington in connection with 

 the testing and standardizing of instrumental outfits, it has been necessary to 

 make special investigations in order to disclose the cause for outstanding dif- 

 ferences between the results as derived from various instruments and various 

 methods, e. g., in connection with the oceanic magnetic work. One of the 

 questions which arose in this connection was as to how exactly the balancing 

 or coupling of the earth's magnetic forces takes place, i. e., whether there is 

 any resultant magnetic force because of which an appreciable pressure would 

 be exerted on the pivot of a compass needle or on the agates of a dip circle. It 

 was found that for some reason, which could not be explained by the present 

 theory of the instruments involved, constants of the ship instruments, as 

 determined by comparative observations on the generally disturbed islands 

 in the Pacific Ocean with the usual land instruments, did not fit precisely the 

 observations made on the ship over the deep seas. 



If in addition to a couple arising from the earth's magnetic forces there 

 also exists a resultant force, then if the magnet were carefully weighed in 

 various positions, e. g., vertically north end up and then north end down, or 

 horizontally north end north and next north end south, dififerences in the 



