236 
NATURE 
[JuLy 6, 1899 
In all matters relating to the re-location of land boundaries, 
where it is frequently necessary to know the precise amount of 
angular change in the direction of the magnetic meridian since 
the first or original survey, the Coast and Geodetic Survey is 
recognised throughout the country as the ultimate authority. 
The amount of money saved to landowners by such authorita- 
tive determinations as the Survey is able to furnish, can scarcely 
be estimated. It certainly exceeds many times the total amount 
to be spent for magnetic work. 
Every effort will be made in the future to multiply and verify 
the secular variation data, and requests for information on the 
part of surveyors will be encouraged in every possible manner 
and true meridian lines established for them. 
This involves the determination of the magnetic elements, 
declination, dip, and intensity at various points throughout the 
land. Exactly how close the stations shall be to each other 
depends upon the special purpose to be accomplished with the 
means at hand, and the magnetic character of the regions in- 
volved. 
A magnetic survey has peculiar difficulties to contend with ; 
for the quantities to be experimentally determined are for ever 
undergoing changes—some periodic, others not periodic. A 
magnetic survey must, therefore, be made to refer to some 
particular moment of time, and such means must be taken as to 
enable one to reduce all the measurements, not only to the 
selected epoch of the survey, but also, as occasion may demand, 
to some other epoch in the near past or in the near future. 
Means must also be taken for the proper elimination of all such 
errors as are to be referred entirely to the particular magnetic 
instrument used, z.e. instrumental errors. 
NUMBER AND DISTRIBUTION OF STATIONS. 
At how many stations it will be necessary to determine the 
magnetic elements? The areas of the countries at present be- 
longing to the United States are, approximately, as follows :— 
United States 3,025,600 square miles 
Alaska een 5773390 a0 
Hawaiian Islands ... 6,250 oe 
Porto Rico 35530 3 
Total 3,612,770 Op 
Hence the area is equal to that of entire Europe, or about 
one-fifteenth of the entire land area of the globe. As magnetic 
surveys have been especially prosecuted in Europe, it will be of 
interest to note the density of distribution of the magnetic 
stations in two recent, fruitful magnetic surveys—viz. that of 
Great Britain, where there was one station to every 139 square 
miles ; and that of Holland, embracing one station to every 40 
square miles. 
Suppose one station is decided upon, on the average, to every 
100 square miles—an end that may be obtained some day—then 
the determination of the magnetic elements would be required 
at 30,000 stations within the United States. At the rate of 
400 stations a year, the magnetic survey, as detailed as this, 
would require for its completion at least seventy-five years. It 
is not well, however, to have a magnetic survey extend over 
such a long interval of years. The errors incurred in reducing 
the observations to a common epoch would greatly exceed the 
errors of observation. 
It is evident, then, that a very large number of observers and 
instruments would be required to complete the survey within a 
short interval, say ten years at the most, or a less detailed 
survey will have to be undertaken. 
The plan of conducting a magnetic survey of the United 
States which appears to be best suited to the present conditions, 
and one that it is possible to carry out within a reasonably short 
time, is as follows :—To make first a general magnetic survey of 
the country with stations about twenty-five to thirty miles apart ; 
then, as opportunities present themselves, to add stations in the 
magnetically disturbed areas. The observations at the ‘‘ repeat 
stations,” made from time to time, will furnish the proper 
secular variation corrections. 
The great advantages of this plan over that of attempting a 
greatly detailed magnetic survey at once, the steady progress of 
which over the entire country, on account of its extent, would 
necessarily be very slow, will be readily perceived. It will be 
of interest, however, to point out that the plan, as briefly out- 
lined, will make it possible, within a reasonable time, to con- 
NO. 1549, VOL. 60] 
struct two sets of magnetic maps for the same epoch, each set 
based upon a different distribution of the stations. An oppor- 
tunity will thus be afforded, as in the case of the magnetic 
survey of Great Britain, to obtain some idea of the accuracy 
with which the isomagnetic lines can be determined. The satis- 
factory solution of this question will serve as a valuable guide in 
future magnetic work. 
Various State geologists, incited by the example set by the 
State Geologist of Maryland, Prof. William Bullock Clark, 
either have already made plans, or are making plans, for detailed 
magnetic surveys of their respective States, in co-operation with 
the Coast and Geodetic Survey. 
MAGNETIC SURVEY OF OCEAN AREAS. 
Provision for the determination of the magnetic elements at 
sea are being made. With the many vessels at the service of 
the Coast and Geodetic Survey, exceptional facilities for this 
purpose will be afforded. In fact, one of the chief duties of the 
Survey is the supplying of magnetic data to the mariner. From 
an economic standpoint this feature of magnetic work is the one 
really of the greatest practical importance. In recognition of 
this fact, the Survey vessels will hereafter take advantage of every 
opportunity to obtain the magnetic elements on sea and on shore. 
MAGNETIC OBSERVATORIES. 
The rapid, successful, and economical execution of the plans 
as above briefly outlined requires the establishment, at certain 
points, of magnetic observatories, where the countless variations 
in the earth’s magnetic force are continuously and automat- 
ically recorded, enabling thus the proper corrections to be 
applied to observations made at stations at any hour of the day. 
The present plans contemplate the establishment of a mag- 
netic observatory near Washington City—this will be the 
Central or Standard Observatory; another near Seattle, State 
of Washington; one in the Hawaiian Islands, and one in 
Alaska. With the co-operation of the observatories at Toronto, 
Mexico and Havana, and with the aid of secondary or 
temporary observatories established as occasion may demand, 
the areas to be surveyed will be fairly well covered. 
It is very much to be hoped, however, that the universities 
and colleges in the United States will seriously consider the 
establishment of magnetic observatories. Many an institution 
which lacks the means of making a reputation in astronomical 
work, could still afford to inaugurate useful work in terrestrial 
magnetism. 
The United States stands at the bottom of the list of civilised 
countries possessing magnetic observatories. Almost every 
European Power of note maintains, not only one, but several 
permanent magnetic observatories. France has four already 
established, and four additional ones in process of erection ; 
and progressive Japan, with its small strip of territory, has six 
continuously operating magnetic observatories. 
The recent International Magnetic Conference recommended 
the establishment of a magnetic observatory at the Lick Ob- 
servatory. It is earnestly to be hoped that this suggestion will 
be carried out. It is unfortunate that the San Antonio ob- 
servatory in Texas had to be abandoned. A permanent 
observatory should be re-established in this locality. 
The scheme of work for the Coast and Geodetic Survey 
observatories will embrace, in addition to the regular magnetic 
work, observations in atmospheric electricity and of the electric 
currents within the earth. Such observations can be carried on 
with practically no additional cost, and yet add greatly to the 
value of the observatory work. Arrangements will likewise be 
entered into with the Potsdam Magnetic Observatory for the 
making of strictly simultaneous observations of a special 
character. 
The plan of referring the initiation and prosecution 
magnetic work in America to such a well-organised department 
as the Coast and Geodetic Survey, the work of which is 
recognised universally as of the highest order, will readily 
be seen to have decided advantages. In the first place, the 
machinery for carrying on the work is already to a great extent 
inexistence. The observer engaged in geodetic or astronomical 
work can frequently include to advantage magnetic observations, 
and thus can often be saved the chief cost of magnetic work— 
the occupying of stations. Again, the care and refinement with 
which the geodetic and astronomical work of this bureau is 
carried out will ever be an incentive to keep the magnetic work 
of the same high order. 
