Dr, E. Nawmann—Magnetism and Earth Structure. 589 
make the following remarks: A kind of break of the isogone occurs 
between Sado and Sendai. This must be of special interest, as a 
geological dislocation line runs across Japan in this region. The 
irregularities are also referred to in a later pamphlet on magnetism. 
As regards Dr. Knott’s curves—although some details of declination 
may be questioned—I think they are a sufficient proof that the distri- 
bution of magnetism bears some relation to the great lines of geological 
structure.* 
When I undertook the Geological Survey of Japan, of which the 
magnetic survey was part, the steps taken were guided by previous 
experience. 
The bulk of mariner’s observations were gone through, and Ino’s. 
field books and maps consulted for compass-measurements. These 
studies enabled me to select the stations at which Mr. Sekino’s 
observations were subsequently taken, in accordance with a definite 
scheme. 
The Sado sinuation is roughly indicated on a small map published in 
1882, and from my magneto-tectonic map (Plate X1X.) it will be seen 
that the selected stations keep fairly close to the ascertained magnetic 
curves. These facts are sufficient to show that the arrangement of 
stations was made with the utmost care. I am afraid that Dr. 
Knott’s stations were not distributed so judiciously. It is greatly 
to be regretted that the second magnetic survey of Japan was 
carried out so independently, and without the valuable hints which 
might have been derived from previous investigations. Not even 
the field books of the Geological Survey were consulted. These 
books contain sketches by which the exact position of every station 
can be easily determined, and in accordance with the practice of 
Lamont the topographical data necessary for the redetermination 
of the places of observation were ascertained, in order that future 
observers might work on the same spots. 
From the memoir on the second Magnetic Survey of all Japan 
we learn that of the 81 stations taken 27 can be regarded as 
coincident with stations of the previous survey. A few of these are 
only roughly coincident. I should digress too far by stating fully 
the reasons why I determined that the stations should be on the 
route followed by Messrs. Sekino and Kodari; it is sufficient to say ~ 
that the test offered by the second Magnetic Survey justifies their 
distribution. At the same time, I cannot avoid stating that the 
new observers should have felt it their duty to devote special at- 
tention to the most interesting regions about the Fossa Magna, and 
between Sado and Sendai. Dr. Knott considers it very important 
to fairly distribute the stations over the whole country, and that it 
is necessary “‘to give volcanoes a wide berth, as these have been 
shown by previous observers to be a great source of disturbance, 
1 There is something very striking in Dr. Knott’s representation. The centre of 
the great loop of 4° 20’, which will be noticed in the main island, coincides with the 
intersection of the great longitudinal and transverse fissures (Fossa Magna) of Japan. 
His curve of equal total force, and that of equal horizontal force, also prove that the 
Fossa Magna has some influence on the magnetic curves. 
