210 THE COMMERCIAL GYROSCOPIC COMPASS. 
peratively due on leaving dock under the conditions in this instance, the magnetic 
compasses being adjusted from the gyro-compass on the way south. 
Within the last four years a large mass of data has been accumulated, from 
daily and other records and logs, of the performance of the gyro-compasses upon 
practically all of the “Seven Seas.”’ These records agree in demonstrating that 
in the gyro-compass we have an instrument entirely free from all of the difficulties 
and disturbances to which the magnetic compass is subject. 
One word as to the theory of the gyroscopic compass: The principle is well 
illustrated by the statement of one of the admirals of the navy, to the effect that 
the writer was the only man of his knowledge who would “lose his job if the earth 
should happen to stop.” It is a fact that the field of force utilized and upon which 
the new navigational instrument depends for its directive power is the actual rota- 
tion of the earth—the steady easterly advance of a point on the earth’s surface. 
This angular motion, although it occurs about an axis some 4,000 miles distant, 
through a well-known gyroscopic phenomenon, compels the gyro wheel to set its 
spinning axis parallel with the axis of the earth. The earth’s rotational force is 
so impressed upon the gyro as to cause this phenomenon to take place with the 
greatest exactness, so that it may be employed as a navigational compass of high 
precision. The phenomenon being a terrestrial one, the pointing is upon the true 
geographic meridian, which is identical with that utilized in navigation; therefore, 
when the compass is properly organized, no deviations or variations exist to com- 
plicate its use. 
The reason for the high precision of the gyro-compass lies in the fact that, in 
addition to its true meridional pointing, its tenacity of purpose or directive power 
is many times that of the magnetic compass. Our battle compass gives 291 times 
the directive power of a 74-inch navy standard magnetic compass (see Comman- 
der T. A. Lyon’s [U. S. N.] “Magnetic Moment of the Compass”). This estimate 
is for the compass in an open field, but down in the interior of a ship the gyro-com- 
pass, surrounded entirely by steel (as is the case with practically all master com- 
passes), has a directive power still very much greater than that of the magnetic 
compass in the same position. 
The same is true with the new commercial compass. Its directive power is 
about one hundred and fifty times that of the same standard navy magnetic com- 
pass, in the positions occupied in both naval ships and those of the merchant marine. 
In the gyro-compass equipments using repeaters, a secondary transmission 
system is employed. This comprises a transmitter, operated by and forming part 
of the master compass, and various forms of repeating instruments, controlled by 
the transmitter, but located at distant points about the ship. The transmitter, shown 
in Fig. 5, Plate 125, is power driven by the compass and is also connected with the 
automatic correction device in such a manner that only corrected readings of the 
master compass are transmitted to the repeaters, which thus read in true bearing 
on the meridian. 
Repeaters, which indicate the true headings of the master compass, may be 
