204 HAUPT—DEEPER NAVIGABLE CHANNELS. [April 2, 
For the foreign commerce there is the illimitable ocean with its 
dynamics—the tides, winds and currents—which are not yet fully 
understood nor utilized. 
The poet Milton has aptly said : 
ss Accuse not Nature, she hath done her part; 
Do thou but thine.” 
This prompts the question, How? It is to answer this query that 
attention will be briefly directed. 
It is well known that engineering, like many other sciences, is 
largely empirical, and that more is learned from failures than from 
successes, for failures are the buoys which mark the channel to 
success. It becomes important, therefore, to review the experiences 
of the past, in which this country is particularly rich, that their 
lessons may guide us in preparing to satisfy the demands of the 
future. With this end in mind, a brief review will be made of 
a few types of harbor improvements, showing their physical features 
and results, and the methods which have produced them. 
ExistTING METHODS. 
The devices in use to-day for the alleviation of the evils of ocean 
bars are twin jetties, dredging and dynamite, either singly or com- 
bined. The theory of the two-jetty system has been so long and 
ably discussed that little need be added further than to state that it 
is based upon the idea of preventing a dispersion of the currents by 
the building up of parallel or convergent training walls to concen- 
trate the discharge upon a single path across the bar. 
The objections to this system are that, being built out from 
shore, the confined waters are projected upon the inner slope of the 
bar, which is pressed» seaward as they advance. Moreover, being 
at a fixed distance apart, they cannot be adapted to great ranges of 
stage, for if adjusted to a normal low-water discharge they will be 
too close to pass the floods without retardation, or the reverse. In 
any case there must result a sedimentation above, within or beyond 
the works, as will be shown later, and dredging must be applied for 
relief, and, furthermore, they reduce the tidal influx. Until within 
a few years twin jetties aided by dredging have been the panacea 
for all classes of harbor bars, regardless of the relations between 
deposits, discharge and the many other conditions affecting their 
