THE COMMERCIAL GYROSCOPIC COMPASS. 209 
The magnetic meridians themselves are so variable, often lying at such large 
angles with the true meridian, that constant vigilance is required to use them at 
all. In fact, the north magnetic pole itself is some twelve hundred miles distant 
from the geographic pole, and is known to be constantly shifting its position. 
In addition to these difficulties, we have operating troubles with the magnetic 
compass, which aggravate the case materially. Among these may, be cited the 
heeling error, which is a constant source of wonder to those unfamiliar with the 
large angle of motion through which the needle persists in swinging, perfectly 
synchronous with the roll of the ship. On torpedo-boat destroyers this heeling 
error amounts to a wide angle of swing when the boats are in the act of rolling, as 
they sometimes are for days, it being nothing short of a miracle that our good 
officers succeed in performing with such an inadequate instrument as the magnetic 
compass the wonderful feats of navigation recorded. 
This heeling error is still greater in the case of aeroplanes. When the use of 
a magnetic compass is undertaken upon aeroplanes, if the machine is put into even 
a mild case of banking, in which it persists for an appreciable period, the heeling 
error of the compass is found to be of such magnitude as to render the compass 
useless. In some instances it will amount to 360°, or around the entire circle, giv- 
ing no clue whatever to the aviator as to the true azimuth or where to stop on 
the turn and straighten out into the tangent. Thus the compass fails him utterly 
at just the critical time when it is most needed. After the tangent is persisted in 
for a sufficiently long time for the compass to settle, then and then only does it 
again become useful. : 
Moreover, the lag or tardiness of action of the magnetic compass is a serious 
drawback to the accuracy of the steering. The tendency of the helmsman is to 
follow this deviation longer than he would if the compass were dead-beat and with- 
out the feature of lag, which gives a constant tendency to a sinuous course and 
contributes materially in several ways to the lowering of navigational efficiency 
and fuel economy. It has been established repeatedly that with the gyro-compass, 
where the lag has been entirely eliminated, so that it does not extend to even 
one-hundredth of a second, ships are enabled to lay a very much closer course and 
materially less helm is used, with the consequence that a considerable gain in 
navigational efficiency is effected, both in speed and fuel economy. 
With the gyro-compass there is never any necessity for swinging the ship. It 
has been found in some of the navies that the gyro-compass, giving the exact geo- 
graphical meridian as it does, serves every purpose for a base line; and-that such 
magnetic compasses as are used upon the ship may receive their adjustment from 
the gyro-compass when the ship is found upon different headings. There have 
been some very interesting accounts of the value of time thus saved—for instance, 
the Invincible on being called from England to the Falkland Islands, reached its 
destination just in the nick of time, with the well-known results, only because it did 
not stop to swing ship for adjustment of the magnetic compasses, which was im- 
