THE COMMERCIAL GYROSCOPIC COMPASS. 211 
located wherever desired on the ship. Various other devices, such as azimuth 
indicators, recorders, automatic latitude instruments, ordnance appliances, auto- 
matic steering mechanism, etc., may be operated from the same circuits that supply 
the repeaters. 
All repeating instruments are positively driven by especially designed step- 
by-step motors, which have no moving contacts in circuit. These instruments 
follow the movements of the master compass with a maximum error of about 
one-twelfth degree and a lag of about one-hundredth of a second. Less than 10 
watts of energy are consumed for each instrument, yet the card is driven with as 
high a torque as 10,000 gm. cms., which abundantly insures the instruments against 
derangement from shock of gunfire. This has been verified by tests upon ships of 
the U. S. Navy under conditions of shock resulting from repeated salvos of ten 
12-inch or 14-inch guns, which caused no derangement of the compass or repeaters. 
Not only is there an entire absence of variation and deviation in the Sperry 
gyro-compass, but extended experience at sea shows that there is no heeling error 
even in the heaviest rolling, this being true for all headings. 
The portable repeater is sometimes very useful, especially in submerged tor- 
pedo fire. It is illustrated in Fig. 6, Plate 125. 
The battle compass is designed to develop a high directive power, because 
its responsibilities are very great—that is, it has to carry along with it a large 
number of auxiliary instruments outside of the regular quota of repeaters. For 
instance, the gyro-compasses that are being furnished to the Admiralty have no 
less than fifteen repeater outlets. For the secondary ships of the navy and for 
the merchant service, no such demand is made upon the master compass, and it 
may therefore be made smaller, so as to involve considerably less equipment, with- 
out having its accuracy impaired within the limits of observation, and consequently 
can be produced at a lower cost. 
Such a compass, however, is more difficult to construct in some particulars, 
because it must be entirely free from disturbances resulting from far rougher 
treatment than is the case with the battle compass. To accomplish this and still 
keep the compass as small as possible, and to prevent these more vigorous dis- 
turbances from decreasing its accuracy, the wheel has been divided into two smaller 
wheels, and a number of other radical changes have been introduced into the 
structure, with the result that a gyro-compass has been produced which is found 
under service conditions to fulfill all of the most difficult requirements. For in- 
stance, one item in the official trials was to run the nose of a destroyer into the 
gale, holding a course for some hours, which produced persistent rolling of the 
vessel through 60° of arc, with the result that the gyro-compass showed not the 
slightest tendency to disturbance or departure from the meridian—it, however, 
being about the only thing on the boat that did not lose its equilibrium. This 
rolling test was only one of a number of severe conditions to which the compass 
was subjected, but with practically no effect upon its accuracy, the entire test 
being under seal and no one being permitted to touch the compass day or night 
through long periods. 
