overcome by placing small buttresses opposite the points pressed upon, as represented by the dotted lines in the drawing; when thus counteracted, which would but slightly increase the expense of construction, the thrust would be of considerable advantage in keeping the joints between the gates and those between the gates and walls of the lock water-tight. The remaining portions of the walls would have the same pressure to sustain in the case of either kind of lock, and therefore no reduction in their dimensions could be made in favor of either of the plans. Estimates A B C are herewith appended of the probable cost of locks of equal size, the one built on the old plan, and the others upon the one submitted by Mr. Bishop. A is the copy of an estimate contained in the annual report for the year 1864, of the State engineer and surveyor on the canals of New York; B is an estimate of a lock of the same size constructed with the proposed new improvements; and C is an estimate of a lock containing water-tight paved slopes in the main chamber instead of vertical walls. The two last have been prepared by Mr. Bishop. Upon a careful examination, neither of them exhibits any marked errors, and a comparison of the costs of the two plans is very decidedly in favor of the invention submitted to the board for its inves tigation. The nature of the contrivance and the advantages claimed, many of which have been referred to and discussed in the preceding part of this report, are chiefly set forth in a circular, of which the following is a copy, issued by Mr. Bishop to different boards of commerce and trade:

Among the various occurrences of the present period of time there is about to be offered for use to the commercial world an improvement to aid in facilitating and economizing in that class of business to such an extent as to revolutionize nearly all the present modes of transporting on rivers and canals. The present canal locks may be rebuilt with good materials so as to form pools of three hundred feet by seventy feet, and place the gates at that distance apart, of such width as will pass two boats side by side; then by one propeller five other boats may be towed in a fleet, and the whole fleet passed through the locks in less time than single boats are passed now by the old plan. The plan to be adopted will enable the public to dispense with animal power altogether on canals, and in the improvement of rivers will supersede the necessity of side-cuts on the shore; consequently steam-power will be brought more into universal

use.

All of the above ideas are based on an unrivaled improvement in canals and river ship locks. The great improvement consists in filling and discharging the water through the locks in an extraordinàry short time, dispensing with miter-sills, giving one foot more of water to an increased size of boats, and operating large gates in wide channeled locks, with as much ease as in narrow ones, with very little difference in time, as w.de gates vent water with an equal proportion in quantity to the variety of sizes.

In rivers, the locks may be completely submerged in floods without the least risk of damage to them; and more, the gates are so disposed of, in case of floods, as to permit the water to flow freely through the whole size of the lock, thereby keeping a clear channel without any other labor; and whenever it is desired to use the lock after the water recedes to the top of the walls, the gates are replaced in the usual position with all the celerity imaginable, and directly stopping the most rapid current rushing through the lock at the time.

With this great advance in such improvements, our great agricultural interests will receive one of the greatest impulses to an onward increased operation in every part of the interior of our country, and the government may possess itself of means of traversing our country with any sized fleets of shipping they will use for defense on the ocean. In proof of what has been stated we will give the results of the passing one lock of a definite size; say a lock two hundred feet long and thirty-four feet wide in the chamber, with ten feet lift, will contain sixty-eight thousand cubic feet of water, and that quantity can be let in or discharged in less than two minutes of time, and thus any larger size of lock will operate in the same ratio of time as it varies in size. One other immense advantage is gained in this improvement by being able to construct these locks of the most durable materials, such as cast-iron gates, &c.

From the above circular it will be seen that the invention consists, in the first place, in a mode or system of operating, economizing, and facil

itating the transportation of the commerce of the country on rivers and canals, thereby revolutionizing nearly all of the present modes, and in the second instance by presenting for consideration a design by means of which the system can be adopted in practice. The device or plan of the invention has already been described, and its several advantages and disadvantages commented upon in great detail; it is now intended to examine the proposed system of navigating canals, which for convenience will be designated the "pool system," to ascertain whether it is a desirable one; and if so, what practicable benefit will arise from its application. This subject is one of vast importance in a commercial point of view, and the proposed change is of such a radical nature and involves so many contingencies, each demanding its own specific weight, that but little more can be here attempted than to call attention to the more important elements of the problem, leaving its solution to those who may possess sufficient data for that purpose. Referring to the requirements of the "pool system," it may be assumed that the width of the whole canal or water-way must either be wide enough to allow two fleets, of description mentioned in the circular, to pass, or the form of either or both must be changed for that purpose. In other words, the fleet must habitually be towed in a single line of boats, and be doubled up on entering the lock, or the whole canal must be made wide enough for four boats abreast, two in each fleet, to move past each other without interruption. The present widths of some of the more important canals are as follows:

According to the "pool system" the above dimensions would have to be increased, and the figures would stand as follows:

Whether the advantages gained by the "pool system" would compensate for the enlargement of any canal as above indicated, would depend upon the amount of traffic and other considerations which it is unnecessary to mention. Should it, however, be found more expedient to tow the boats in a single line, considerable delay must ensue at each lock; a question then arises whether the time thus lost would not be equal to, if not greater than, that which would result from the ordinary course of procedure. It might appear that the fleet could be towed habitually in

two lines, and undouble on passing other fleets; but since the number of boats passed is generally much greater than the number of locks on any canal, this would evidently be less advantageous than the other plan. Where these locks are intended to pass boats from one pond to another, in the case of slack-water navigation in rivers, these considerations would of course not apply, as a sufficient width of water-way is generally to be found in such cases. In the second place it must be taken into consideration that a sufficient quantity of water will have to be supplied to canals with a summit level to make up for the quantity required to fill it and its dependent levels in consequence of the additional "expenditure" due to the greater size of the lock-chambers and pools, and the greater displacement of water by the fleet. This would increase the cost of feeders and reservoirs, which is a very considerable item in the estimate for constructing many of the present canals, and in some cases it might preclude the use of this system altogether. It would also follow that the currents, which always exist in canals from the summit level to the waste-weirs in the lower levels, would be increased in the same ratio. These currents, besides wearing the banks of the canal, retard boats moving against them, more than they accelerate those pursuing the same direction, and consequently cause a dead loss of power. In the third place, as stated in the circular, the use of steam-power must entirely supersede that of horses in propelling boats through canals; unless the requisite number of them arrive at the lock simultaneously, those coming first must be detained until others arrive, otherwise a greater quantity of water must be expended and time consumed in passing one or two isolated boats than would be required for a whole fleet; the prisms of lift and draught, or contents of the lock, would be the same, while the displacement of the boats would be less in the same proportion as their number is less than that of the fleet. While it is probable that steam will eventually replace that of horse-power, still from the present nature of canal traffic the number of boats in a fleet will be very variable and many isolated ones will be continually passing. This will, however, be remedied by the constantly increasing amount of transportation by this mode, as soon as any decided improvement is effected for facilitating commercial operations. There are many and great reasons why extensive improvements of the kind should be inaugurated in the United States; an uninterrupted system of canal and river transportation extending over the entire country has become an absolute necessity both for commercial and military purposes.

When the several causes of disqualification, or disadvantages, do not exist, or where they are small in comparison with the benefits to be gained, the "pool system" may be successfully employed, and there is no doubt the advantages will be fully equal to those claimed by Mr. Bishop in the circular already quoted. The suggestions submitted and the alterations proposed after careful examination and study of the plan of a new lock gate as presented by him for the consideration of the board ordered to investigate it, far from lessening the merits of the invention, are calculated to render it more deserving of attention in the minds of practical engineers by at once removing the objections which might arise against some of the constructive details of its mechanism or the more advanced theories of its usefulness; these, however, have nothing to do with the application of the inventor of the grand principle applied in arranging the gates in the manner presented in his plan.

ADAPTATION OF THE PLAN TO THE WASHINGTON CANAL.

The above conclusions, and the fact that the Washington canal is, at least nominally, under consideration by another board of engineers, by whom a preliminary report has been submitted, would seem to leave but little to be said in regard to another division of the subject of this report, that of "the adaptation of Mr. Bishop's invention to aiding in the construction of a ship canal through the city of Washigton." As it may be considered, however, by others as an auxiliary to a general plan for improving the canal through the city, it would not be irrelevant at this time to record some general observations on this subject. The history, objects, and condition of the Washington canal have contributed a very considerable portion to the literature of the city for many years, and the various reports on the work in question, and projects for its improvement, would form a volume of matter of such magnitude as to render a revision of the whole subject too elaborate to be attempted here, especially as one does not appear to be necessary in this connection. The canal has been used since its construction for two purposes; the one for navigation, and the other as a main, open sewer; it has been the receptacle of the sewerage of the larger portion of the city, as well as of the surface drainage and the debris washed down through the bed of Tiber Creek. In consequence, it has been gradually filling up with a mass of most deleterious matter, and to such an extent as to render it not only entirely useless for the greater part of its length for the passage of boats, but to cause it to become a public nuisance. Attempts have been made during the last two or three years to partially abate the latter by removing a portion of the deposit by dredging, and by flooding the remainder by means of tide gates; but after repeated efforts these means proved to be, as they were intended, only temporary expedients, and cannot be considered as having produced any very beneficial results. The various projects for the permanent improvement of the canal may be divided into three classes: the one proposes to continue the use of it both for its legitimate purpose and as a sewer combined; in other words, to let it remain in its present status; the other to employ it entirely for the transportation of boats and to build a covered sewer parallel to it; while the third plan suggested is to fill it up excepting so much as may be necessary for a proper sewer, and discontinuing its use as a canal altogether.

Mr. Bishop's project belongs to the first of these classes. In general terms he proposes to extend the canal up the river to Georgetown; to cut off the present sharp bends at different points; to place locks at its junction with the Potomac and Eastern Branch, and to replace the present permanent bridges across it by turning or draw bridges, in order to allow vessels of all descriptions to pass. In addition, as part of this plan, the Georgetown or Virginia channel of the Potomac is to be closed, and thus divert the tide of commerce from its present channel, and direct it through the new one. He also contemplates to clear the canal and keep it free from objectionable matter by opening the gates and completely flooding it at certain stages of water in the river. Without entering into the details of this project, it may be stated that the requirements of a navigable canal and a suitable sewer are incompatible, and that in general whatever tends to improve the one necessarily injures the other. For example, a good sewer should have a declivity of at least one foot in a thousand, while the canal should be as nearly level as possible; the sewer should be no larger than is requisite to carry off all the semi-fluid mass or water that can find its way into it from its lateral

branches or from surface drainage, while the larger the section of the canal within reasonable limits the better; the sewer requires to be covered while the canal remains open. The board cannot, therefore, recommend any project in which it is contemplated to use the same channel for the two purposes, however feasible the details of such an undertaking may be. It is a well known fact that along the wharves of all large cities there is a constant deposit from the contents of the sewers, which necessitates either almost continuous dredging, or the extension of the piers beyond its influence.

There is no doubt that any canal, receiving the constantly accumulating matter from a great portion of the sewerage of a large city, must be filled sooner or later unless there is a very strong and constant current through its entire length. In this case there is no possibility of producing such a current without extending the canal up to some point at or near the Chain or Little Falls bridge, some three miles above Georgetown, even then the velocity of water at the sides and bottom of a long narrow channel is so much retarded by friction, that while there might be a sufficient strength to the current at the middle of the canal, a deposit would probably form on the sides and bottom. This would take place even in a constant current when the floating material is kept in motion and scarcely allowed to settle and become compact, how much more then would it obtain when locks were introduced, and the force of the water allowed to exert its influence only at intervals. That part of Mr. Bishop's project, which contemplates the substitution of turning or draw bridges for the present permanent ones over the canal cannot reasonably be entertained. The canal now separates the main portion of the city from that section fronting on the Potomac, along which at the present time the larger number of wharves have been constructed for commercial purposes. To interfere or interrupt the constant travel and hauling of heavy freight on the streets leading from them would prove a very great injury to trade and the improvements now projected in their vicinity. Even should benefit arise to one part of the city by enlarging the dimensions of the canal so as to enable sea-going vessels to enter, it would scarcely compensate for the expense of the undertaking, and the damage that would be sustained by another and a very rapidly improving portion. Should the money necessary to execute such a work be applied to dredging and opening the old Washington channel along the whole water front of the city, it would prove a more profitable and beneficial expenditure. A long and continous line of wharves, extending from the Arsenal Point to the foot of the Little Falls, could then be built. The closing, as intimated in the method of improvement referred to, of an old and well established channel like the Georgetown or Virginia one, for the purpose of opening another and a more circuitous one through the heart of a large city, would scarcely meet with very favorable consideration in any point of view; the only practicable and intelligent plan of operations is to accomplish by mechanical means what nature originally designed should be the case, the reopening of the old channels as they existed before any encroachments were made upon them, or any obstructions allowed to be interposed to their detriment. In closing this division of the report, the board cannot look upon the facts just stated as being in any way discouraging to those interested in the improvement of the Washington Canal. If it cannot be made to serve two purposes, there is no reason why it should not be made useful in accomplishing one good result, one object well accomplished will certainly prove more profitable than two imperfectly executed. It is susceptible of a mathematical demonstration that should either the second or third