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ase some drift-material would be carried the project of the engineer, because the
by waves and surf-currents around the useful life of his works is more or less
jetty heads, and would subside in the dependent thereon.'
deep water between them, to be swept “As no works can be expected to stop
out by ensuing ebb-currents, and dis- this movement of drift-material for any
posed of to the northward or southward, great length of time, they should, if
according to the direction of the storm. practicable, accommodate themselves to

“This movement of sand was referred it under conditions of a permanent charto in my report on the improvement of acter. Those proposed are designed to the Fernandina Bar, submitted April 15, do this, by allowing the drift-sand to 1876, from which the following extract move from one part of the bar to the is made:

other, in much the same manner as now, “As a moderate assumption, a north- never remaining in the jetty channel easter of three days' duration might be longer than a few tides, and never findexpected to lower the north shoal four ing a resting place anywhere that the inches within the area covered by the next storm may not disturb.” breakers. The greater part of the eroded From the forthcoming report we learn material, amounting to upward of 516,000 that: cubic yards, would doubtless be dis “During the fiscal year just closed, tributed along the south shoal during the work of putting down the apron

of the progress of the storm. If the waves the North jetty was continued, and the should subside, or a southerly or south- construction of the South jetty was easterly storm set in before the bar begun. channel had returned to its normal con “The foundation matters of the North dition, the mate ial subsequently carried jetty continued to be made after the modi

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out would not reach the south shoal, but fied design (see Fig. 2). Another modi-
in the former case would remain near the fication in this contract was made August
outlet on the outer slope of the bar, and 19, 1879, under which a mattress was in-
in the latter would be carried back by serted as a hearting in the rip-rap super-
the waves to the north shoal. If as structure of the apron, in order to get
much as one-fourth of it remained in the increased height by the use of a material.
bar channel, between the inner and outer less costly than stone.
18-foot curves, a few severe storms, such “This second mattress, which is in all
as frequently occur within the period of essential features like the lower one, has
a single month, would entirely destroy a prescribed thickness of 18 inches in
it, by filling it up to the level of the the finished jetty, and is paid for in the
shoal on either side.

work at the rate of $5 per lineal foot of
“. It would appear, therefore, that mat, fifty-four feet wide, equivalent to
millions of cubic yards of the material $ 1.663 per cubic yard. When the bot-
composing the bar might be shifted back tom mattress has been sunk and loaded
and forth from one side of the channel with stone to the depth of a few inches,
outlet to the other, during a single as evenly distributed as possible, the
season, without causing injury to the second mattress is sunk in its place, and
channel by shoaling, and without produc- the balance of the 2 feet layer of stone,
ing any changes in the form and location required by contract on the apron, is
of the bar itself that might not entirely placed upon it.
escape the notice of the most careful “ The width of the second mattress is
surveyor. And yet this shifting of uniformly less, by 32 feet, than of the
material, of which no evidence may be one at the bottom, in order that the rip-
left behind, should enter as an im. rap superstructure laid with flat slopes
portant, if not a controlling, function in will cover it and protect the ends of the

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logs from the ravages of the teredo. by beginning the construction of the Less apprehension of injury from this South jetty. cause is felt for the bottom mattress, for "Among the specifications of the conthe reason that from its position, direct- tract for the work to be done this year is ly on the bottom, it is likely to become one for mooring chains of wrought iron, quickly covered with sand whenever there to be afterwards used in securing the is any tendency to till ut all.

top layers of stone on the finished jetty, “When the apron of the North jetty against removal by the waves, will be had attained a length of about 5430 feet attached to the logs of certain mattresses from the shore, in only 5 feet low water at intervals of 40 to 50 feet along the soundings on the inner slopes of Drunken line of the jetty where most exposed to Dick Shoal, work was suspended on ac- the force of the waves. The lower end count of rough water and breakers, and of each chain terminating in a ring will resumed on the seaward slope of the be supported by a buoy, spar, tripod or shoal, at a point on the amended curve otherwise, so that it will not become of location, leaving a gap of 1647 feet to covered up with stone, and can be found be filled in hereafter.

at any time. The chains will be galvan“If this shoal, which at present shows, ized in the best manner. on some portions of it at least, indica “These galvanized mooring chains tions of considerable stability, shall con- will be what is known as chain cables, tinue to resist abrasion and wear, after and will be of such sizes, not less than 1 the work on each side of it reaches the inch, nor more than 17 inches in diamrequired height, there will be no special eter, and of such lengths, and attached need of re-enforcing it, or of raising its to such mattresses, and at such distances surface artificially. If, on the other from the sides thereof as the engineer-inhand, it yields under increased currents, charge shall direct. or wherever it does yield and wear away “A second course will probably be from any cause, increased depths will be placed on some portions of both jetties the result, and the breakers will doubtless before, or during the coming Autumn. subside to such a degree that there will “It is not the present intention to give be no special difficulty in laying the work. the base of the south jetty, during this

“During a spring tide of considerable fiscal year, its full width where it crosses range in the month of July, 1879, a large the main ship channel in about 40 feet portion of the shoal was laid bare at low low water soundings. It seems desirable water, and part of a wreck which has that as great height as possible should doubtless been there for some years was be gained in this deep water with the discovered on it, indicating that the ma- funds now available, and the work will terial of the shoal has considerable firm- therefore be laid in two or more courses, ness and tenacity.

the bottom one being about half the re“So far as known, this precise locality quired width. It is possible that the has never been examined by boring. sand will fill in so rapidly that the full

“When work under the first contract width of base adapted to this great depth was finished on the outer end of the will not be needed. When the bottom jetty, the use of the second mattress, course, rising to a height of about 2 feet 8 which is not adapted to the thin courses or 9 inches has ceased to accumulate sand, of the later contract, was also discon- the second course will be laid, and after tinued.

that perhaps a third course in some “The prosecution of work upon the places. North jetty since the 10th of May, and “An inspection was made a few days upon the South jetty since the 23rd of before the close of the fiscal year, of the April, has been in conformity to a con- entire line of work on the north jetty. tract dated September 6, 1879.

No settlement was detected in any por“Under this new contract the engineer- tion of it, except in the deep water of in-charge has the power to regulate the Beach Channel, where for a length of height of the jetty by laying it in one or 200 feet a subsidence seems to have taken more courses, and the work can be pros- place varying from 1 to 3} feet, the imecuted by extending the North jetty, and mediate cause of which has not been asraising it higher at certain points, and certained.

“On that portion between Drunken jetty, however, a marked increase of Dick Shoal and Sullivan's Island, the depth, amounting to three feet, over ends of the logs are reported to be well considerable areas, has taken place durcovered with sand, except when the low ing the past year, which is to be at water depth not exceed 8 feet. On tribute

On tributed to the direct action of the jetty. former examinations the timber even in The changes were more rapid as the this shoal water was found to be covered. jetty advanced. The effect has been to The cause to which its present exposure move the inner end of the swash channel is to be attributed, cannot be positively northward. It may be expedient to stated.

assist, by dredging, this developed ten“South of Drunken Dick Shoal the dency to scour along the line of the proends of most of the logs remain uncover- posed channel, when the time for such ed, and exposed to the ravages of the auxiliary work shall have arrived. teredo.

“During the month of June, 1879, “It is proposed to cover all the exposed arrangements were made to cover the timbers with rip-rap stone, and steps exposed logs, north of Drunken Dick have been taken to procure it as soon as shoal, with ballast stone and brick-bats ; practicable.

but the sand eventually collected along "It is found that sand accumulates the margin of the work sufficiently to very slowly around the ends of the logs, afford the requisite protection. Only 18 on the south jetty. No settlement is re- cubic yards of brick and stone were ported there.

placed on the work under this agreeA few months before the close of the ment. fiscal year, I had an opportunity to ex “During the present fiscal year, it is amine the shore end of the north jetty, expected that both jetties will be exat an unusually low stage of water, and tended, and, in some places, raised to a I found that the rip-rap stone, placed higher level under the existing contract, there 15 months before, had become so and others to be entered into hereafter, firmly cemented together with barnacles by methods the same, or substantially and other shell-fish accretions, as to ren- the same, as those hitherto followed ; der the mass remarkably dense and com- and, if deemed advantageous, some pact.

dredging will be done by the United “It seems quite improbable that the States dredge steamer · Henry Burden,' stone, even on the most exposed part of along the line of the proposed channel.' the work beyond the bar, will ever be washed off or moved by the waves, if it can once be consolidated in this manner COAL INDIA.-Theodore W. H. by the molluscan growth of a single Hughes begins a paper on the coal

fields of India by saying: “It will “It may be hoped, therefore, that re- doubtless surprise many to learn that course to the mooring chains, for holding both in the superficial extent of its coal a line of large stones, linked together measures and associated rocks, and in along the crest of the work, for which the actual amount of its coal, India is provision was made in the contract, will surpassed by few countries, and that not be necessary.

with respect to the size of some of the “The work has not yet reached that seams it stands pre-eminent in the hisstage when increased depths can be ex- tory of mining.” Even the United pected in the swash channel, which, oc States cannot boast of seams 100 feet, cupying the proposed gap between the 120 feet and 160 feet thick, like some two jetties, is, nominally, the one to be that occur in Bengal. He calculates improved.

that the coal fields of India cover 35,000 " But it is neither expected nor de- square miles, and according to estisired that the improved channel will mates drawn up by Dr. Oldman there occupy the line of the present one. It is cannot be less than 20,000,000,000 tons a crooked channel lying at an average of coal in the Empire. Much of the distance of not less than 1,400 feet from material, however, is of an inferior the line selected for the North jetty. On quality and fit only for very rough use. the shoals lying between it and that -L'Ingen. Univ.

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summer.

THE VALUE OF THE STUDY OF THE MECHANICAL

THEORY OF HEAT.

By ALFRED R. WOLFF, M. E.

A Paper read before the American Society of Mechanical Engineers, November 5th, 1880.

I IN presenting a few remarks on the signed to do the desired special work, Value of the Study of the Mechanical or, in other words, to that department Theory of Heat, I am imbued with the which relates to the generation of the knowledge of two facts: of the import- working fluid or motive power, and the ance and value of the study on the one work performed by the medium of such hand, and of, in general, a lack of proper fluids in prime movers. It is on this appreciation among engineers of this ground that I would urge the more point on the other. There are doubt- general acquisition of the science of less few among educated engineers thermo-dynamics, and to insure concisewho would not admit that the acquisi- ness as well as a ready conception of my tion of any form of knowledge is of views, I will only briefly outline the value, not only as a training of the mind thoughts, giving as it were their direcbut as an addition to our understanding tion, and leave it to you to give them of the laws and working of the universe force, that is, to develop them more and mankind; few who would deny that fully as your own understanding and the study of literature, of social or experience will best suggest. politico-economic sciences would be of Thermo-dynamics or the Mechanical benefit to them, though of limited influ- Theory of Heat is, as the name implies, ence in the practice of their profession. the science of the laws of heat consid

From personal experience, as well as ered as a form of energy. It is based from the experience of others, I am led upon two great, general laws, the one to believe that engineers, as a class, look that all forms of energy are mutually upon the knowledge of the mechanical convertible in certain exact, invariable theory of heat not much unlike than that equivalents, the other that the quantity of the department of “belles-lettres,” as of energy in a homogeneous substance possibly adding to refinement, to a is equal to the sum of the energy of its broader view of things in general, to a component parts, and that equal parts fair drilling of the mind, but of no prac- of homogeneous substance when tical or only slight practical value in the undergoing a change of, or exerting, ordinary, or even extraordinary, exercise energy undergo like changes, and exert of their profession. I am not prepared like effects. The application of these to say that were the grounds above two fundamental laws of energetics to enumerated the only ones upon which heat constitute the determination of the the study could be urged, that a strong two general laws of thermo-dynamics, argument in favor of its more general which are the basis of the whole science, introduction could not justly be main- and of which the science is in fact but an tained; but this question does not arise extension and application to forms of since the more general introduction of heat energy, latent or active, met with the science can be presented to the engi- in nature and valuable in practice. For neer on the ground of direct, practical after all what is theory but practice utility, for the purposes of correctly reduced to a connected system of laws appreciating and increasing the effi- or principles. Without facts, without ciency of a large department of his pro- phenomena, in short, without practice as fession, that department which treats of a foundation, how could theory ever be the transformation of the latent or conceived or established? In ordinary active forces or powers of nature in a discussion but little attention is paid to form suitable for application as motive the distinction between theory and hypopower for utilization in machinery de-thesis, and nothing has proved more dis

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astrous to a general appreciation of those who have mastered the difficult theory than the repeated misuse of the with scornful or doubting eye, until the term. Theory is based on facts, hypo- achievement of the difficulty by the few thesis on speculation, hypothesis changes has brought forward such valuable reto theory when speculation changes to sults, such striking truths, so influences facts. The two special laws of thermo- the ordinary experiences and our condynamics, upon which the whole science ception of facts in nature or in our prois elaborated, to which we refer are: fessions, that the worthiness and value that heat is convertible to other forms of the attainment can no longer be of energy in the relation of what is denied and must be definitely accepted. known as Joule's equivalent, that is, That point has now undeniably been that one thermal unit (the quantity of reached in thermo-dynamics, and the heat required to raise one pound of sooner we concede it the better. The water at 39.4° Fahr., one degree in sooner we admit that we must study and temperature) is equal to the energy re- explore the science of heat energy in its quired to raise 772 lbs. 1 foot, or that higher form, the sooner will we advance 772 lbs. falling 1 foot will develop suffi- in our profession and contribute to its cient heat to raise 1 lb. of water at its progress. It will be my aim to recall a greatest density 1 degree. The second few of the practical applications in engiis that if the total actual heat of a homo- neering of the principles which thermogeneous and uniformly hot body under- dynamics has established, and thus to go a change or exert energy, equal parts give an illustration or rather indication of the body will undergo equal changes of its value. But before doing so to be and exert like effects, the sum of the strictly conscientious, I must refer to effects of the component parts being the difficulties to be met with in the equal to the total effect. This law is study in its higher form. Professor more popularly identified in the form of McCulloch says: “Any one acquainted Carnot's theorem, a special application with only the elements of analytical

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geometry, and of the fluxional calculus, to heat engines, that 9-9, or should find no difficulty in understand

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ing all it contains. In this country, is the limit of efficiency of such engines, however, scientific education, as well as and that the test of a perfect engine is classical, has unfortunately retrograded; its reversibility. I and T represent re- and superficiality is the fashion of the spectively the quantity of heat and abso- day. Hence, some anxious for scientific lute temperature of the (any) fluid when knowledge, with the least labor and in leaving the generator, and, and T, the shortest time, imagine it might be respectively, the quantity of heat and well in scientific literature to dispense absolute temperature of the fluid when with the calculus. To them no better given off to the refrigerator; 9-9, when advice can be given than to begin by entirely converted into useful work caus- studying it thoroughly, if they would ing the engine to become theoretically reasonably hope ever to comprehend perfect.

much which would otherwise be uninThe above outlines the foundation and telligible.” framework of a great science. It is These elements, however, must be strong and simple, and in its strength firmly fixed in the mind, and thermoand simplicity beautiful. The structure dynamics may justly be considered a and superstructure are equally strong, thorough test of such a knowledge. equally beautiful, but not, however, When beginning the study of the subequally simple. If this were the case ject, I thought I had fairly mastered there would be little need of the pre-calculus, while engaged in its acquisisentation of papers of this kind, for the tion I found I was a mere novice, and great value of the science would be uni- such too has been the experience of a versally acknowledged. It is a common few of my friends who have already proexperience that the mass of mankind gressed and done good work in the primarily pronounce that which is diffi- science. But let us not be deterred cult to attain as not worthy of attain- from the acquisition of a valuable subment, primarily too often look upon ject because of its difficulty. This

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