VAN NOSTRAND'S LIBRA ILLINOIS. ENGINEERING MAGAZINE. NO. CXXI-JANUARY, 1879.-VOL. XX. THE PHYSICS OF THE MISSISSIPPI RIVER. A LETTER TO THE EDITOR OF VAN NOSTRAND'S MAGAZINE IN REPLY TO THE ARTICLE OF JAMES B. EADS IN THE SEPTEMBER NUMBER. Sir: In the September number of your nothing to do with it-was conclusively Magazine, a Review of the Report upon decided in, the negative by the long series the Physics and Hydraulics of the Miss- of observations recorded in the Physics issippi, by Humphreys and Abbot, ap- and Hydraulics of the Mississippi. Čapt. peared over the signature of James B. Eads, with various adjectives which add Eads, C.E. He states at the outset that nothing to his argument, denies the truth he desires to reach the general intelli- of this deduction, and asserts that it is gent public, rather than scientific read- based upon fallacies and blunders made ers. Although the Mississippi report by us in discussing our observations. was prepared for professional engineers, The accuracy of the latter he does not and its conclusions will stand or fall by dispute. their verdict, I ask space in your Magazine to expose some of the errors of this popular review. Our analysis of these observations, stated in brief, consisted in plotting two curves, of which the common abscissas were times; and the ordinates, respectively the mean velocity of the river in feet per second, and the corresponding number of grains of earthy matter held in suspension by one cubic foot representing the average for the whole river. If the latter quantity were a function of the former, the forms of the two curves would exhibit a certain symmetry; This was not the case, the amount of sediment per cubic foot when the river was flowing most rapidly being often no more than at the lowest stage. These curves happen to be very unlucky for Capt. Eads' professional projects; for they overturn the theory upon which he proposes to dispense with levees, to improve the navigation of the upper river, and, in one word, to control the appropriations which Congress may reverse, Capt. Eads' theory falls to the grant for the lower Mississippi. The ground. world is not wide enough for them and That the figures plotted by us correcthim, and they must be removed from ly represent the quantities in question is his path. Invoking, therefore, the di- evident when we consider what they are. vinities of Dynamics, Force, Matter, The mean velocity is the mean of the Space and Time to aid in raising a cloud horizontal velocities of every cubic foot of confusion over a very simple question of the river. The amount of sediment of mathematics, he makes a desperate was measured by collecting samples of assault upon our method of reasoning. water from three stations-one, 300 feet Not to follow him through several pages from the East bank, where the high of this style of writing, which, although water depth was 100 feet; another in the perhaps effective with the popular audi- middle, where the depth was 100 feet; ence to which he appeals, will be passed and the third, 400 feet from the West over by professional men, let us examine bank, where the depth was 40 feet. The his final conclusion. It is, that the ordi- total width was about 2400 feet. One nates of the sediment curve must be hundred grammes of river water were multiplied by the corresponding dis- collected daily, Sundays excepted, at charges of the river, before they can be surface, mid-depth and bottom, at the compared with those of the mean velocity curve. two deep stations; and at surface and bottom at the other. The figures plotted in our curves represent the mean weight of sediment per cubic foot for the entire river, computed by averaging the results from the eight stations. This The absurdity of this proposition has been so clearly pointed out by Mr. R. E. McMath, C.E., in the Engineering News for February 28, 1878, that it is needless to repeat the elaborate algebraic demon-averaging is legitimate, because the disstration by which he arrived at the conclusion that "mathematically this step is a blunder which would disgrace a boy in the junior class of our High School.' tribution of earthy matter held in suspension is remarkably uniform throughout the river, as is proved by the following yearly totals: DISTRIBUTION OF EARTHY MATTER. Station. High Water Depth 100 Total grammes collected in one year. Mid- Bot Surface. depth. tom. 15.302 17.552 17.880 15.156 18.977 19.538 13.845 20.070 Suffice it to say, that the quantity under discussion is not, as Captain Eads argues, the total mechanical work performed by the river, which of course depends upon the number, as well as upon the supporting power, of all the cubic feet of water in motion; but the force which neutralizes the gravity of the earthy matter held in suspension. If Near East Bank. 100 this force be less than gravity, a deposit Near Middle.. must occur; if it be equal to gravity, the Near West Bank water will be charged to its maximum supporting capacity with earthy matter; The bearing of these figures upon if it be greater than gravity, an additional amount of earthy matter may be added Captain Eads' theory as "modified by without causing a deposit. Now, Capt. depth" is too plain to need comment. Eads' theory confessedly requires that To recapitulate the foregoing views in the water be always charged to the maxi- more concise and mathematical language, mum capacity due to its velocity. The the problem to be studied experimentally point, then, for observation to determine, is, whether: S=ƒ (V). is, whether there be any fixed relation between the earthy matter suspended in In which S denotes the force which, a unit of volume, and the horizontal opposed to gravity, maintains the earthy velocity of that unit of volume. If any matter in suspension; and V is the horifixed relation existed between these zontal velocity of the volume of water quantities for the Mississippi, our curves supporting said earthy matter. Now let would reveal it; but as they show the us see what our critic proposes to do. If he were not so bitterly in earnest about wonder whether, if Capt. Eads' had the problem, his blunder would be funny. noticed this ugly fact, he would have He actually multiplies one member of the announced that, according to his investiequation of which the truth or falsity is gations, these data "bear excellent testito be experimentally decided, by the dis- mony to the care with which Messrs. charge, which is nothing but the product Webster and Fillebrown conducted the of the area of cross section (a) by the experiments at Columbus." mean velocity, (V); and leaves the other member unchanged, giving: SaV=ƒ'(V). BED OF THE MISSISSIPPI. The second main issue which Capt. Eads raises with our report, is in respect to the nature of the bed of the Mississippi. In this matter, he sets up a man of straw, and after overturning him, claims by so doing to have refuted our And he then proceeds to congratulate himself, and to apply adjectives to us, in honor of the surprising discovery that, after he has introduced V into the first member, that member thus modified can views. be proved to be a function of V! As an example of the reckless mis It would be easy to point out many statements of facts which characterize other minor errors in this division of the whole review, I quote the following Capt. Eads' review, but after this ex- paragraph: posure of the fundamental fallacy upon which his whole argument rests, it would be wasting time to do so. Our position in the matter simply is, that the earthy matter which the river holds in suspension is chiefly that brought to it in suspension by its tributaries; and that if the amount they supply at any time be less than the velocity would support as is usually the case in floods from the comparatively clear tributaries, like the Ohio-the water remains under-charged. Capt. Eads' claims:"If the reader will bear in mind that the water is charged with sediment according to its velocity, and that it flows through a bed of precisely the same kind of material it is carrying in suspension, and that if its velocity is increased it will take up a greater charge from its own bed, or if its current be slackened it will drop some of its charge in the channel, and add to its bed, he will understand the important part which the speed of the current performs in the problem." Perhaps in thus committing himself, Capt. Eads' did not know that at Columbus, Ky., 20 miles below the mouth of the Ohio, the waters on the East side of the channel, which have issued from that river, although moving side by side, and with equal velocity with those from the Missouri on the West side, contain only about three quarters as much earthy matter in suspension. This fact, stated in the Mississippi Report, is proved by eight months' daily observations at Columbus. It would be ill-natured to "By reference to pages 135 and 137 [Mississippi Report] it will be seen that this extract contains an astonishing exaggeration. Instead of three years, the current and sediment observations only occupied eight months at Columbus, and one year at Carrollton. "When we remember that the junior author of the report on the Mississippi River was a prominent member of the Levee Commission, and that the senior author, as Chief of Engineers, warmly endorsed its report, it is difficult to reconcile this careless statement with the unusual scientific exactness which required four decimals to record their measurements of the current." Turning to the page next preceding the one mentioned, we find a table giving in detail the results of the two years of sediment observations made by a party of the survey at Carrollton; and on page 142, another, giving the details of a continuous series of nearly three months' observations, made by Prof. Riddell. These with the eight months' record at Columbus, sufficiently sustain the accuracy of our language. After such an exposure, it is sufficient without devoting space to other instances of similar inaccuracy in this Review, to ask the reader to apply the old maxim, ex uno disce omnes," and take the precaution to refer to the report itself, before accepting as trustworthy Capt. Eads' statements respecting its contents. This precaution is particularly necessary in order to understand our real position in relation to the bed of the break, just above the head of the Passes, river. Capt. Eads endeavors to convey introduces anomalous features, which to the reader that our views rest solely prevent occurrences there from having upon a limited number of soundings in any legitimate bearing when applied to the river itself, and that all the informa- the river above. The great Bonnet Carré tion we possessed on the subject is re- Crevasse, above New Orleans, has been ported in full in Appendix C. Neither of open since April, 1874, discharging an these ideas is correct. It is nowhere immense volume of water at every high stated, nor is it true, that Appendix C stage of the river; and yet no well-marked describes every sample brought from the shoaling has occurred below its site. bottom. In the work done by me, per- Capt. Eads may perhaps venture to deny sonally, in which I used one of the this statement, which is fatal to his thetransits on the bank, it frequently hap-ories; but the facts set forth in the Repened that when the boat brought the port of the Commission of Engineers, specimens for inspection, some uncertain- ordered by Congress to investigate and ty would exist as to the exact soundings report a plan for the reclamation of the in which individual specimens had been alluvial basin, fully confirmed by later secured. In such cases, the samples surveys, speak for themselves, and estabwere not bottled and no specific entry lish my position. was made, but the general nature of the bottom was carefully noted, and this information was used in the final report. I must now refer to the single paraCapt. Eads might as well demand that a graph which has called forth this reply botanical collector should exhibit speci- to Capt. Eads-his other statements, I mens of a plant gathered from every think, might have been safely left unanlocality in which he discovered it, as to swered, to be judged by professional apply such a criterion to our work. men. THE ST. LOUIS BRIDGE. It must be apparent to every reader, that the personal animosity constantly exhibited by Capt. Eads toward the Chief of Engineers, and which marks every page of this review, unfits him from taking a fair view of the subjects discussed. This has led him not only to misrepresent the real issues, but also in the following paragraph, to introduce one entirely irrelevant: But if this kind of criticism is unfair, for a still stronger reason is the unfound ed assumption that our views are solely based upon soundings in the river itself. In the report and appendices will be found stated at length many facts bearing directly upon the geology of the region traversed by the river, and which, from their wide range and perfect accordance with each other, will, it is believed, have great weight with any unprejudiced "A few years ago the Chief of Engineers mind. Capt. Eads' whole argument on of the United States Army, being equally this point is that of a lawyer endeavoring as well convinced that the steamboat to raise quibbles, rather than that of a judge stating the truth in an impartial manner. Readers who desire to study the subject should refer to the report itself, where the arguments are stated in as concise language as can well be used. They proved convincing to every member of the Commission of Engineers to which the subject was officially committed by Congress; and that they do not harmonize with Capt. Eads' wishes and theories, is our misfortune, not our fault. One other point. Lest Capt. Eads' assertion that the shoaling of the bed of the river below Cubitt's Gap proves that crevasses cause a deposit in the channel, be accepted as true reasoning, I will simply say, that the location of this smoke pipes. were, like the bed of the river, unyielding in their nature, and that they were too high to pass under the bridge which spans the Mississippi at St. Louis, accordingly recommended that a canal with a drawbridge, through the bridge approach, to accommodate these unyielding smoke pipes, should be dug round the end of the bridge in the ancient geologic blue clay in Illinois, at a cost of over three million dollars! The fact that the river was proved by 'a glance at the two diagrams to be always undercharged with sediment, was an assurance that the canal would be a success and would not silt up. But Congress did not look with favor on this plan. Doubts as to the unyielding nature of |