noticed that larger blocks are often used on the margin of carriage roads than in the more frequented middle of the way.

Care seems to be taken to lay the courses at right angles to the line of travel. In a few streets they are laid diagonally, but in only a few. The stones seem to be laid on a bed of gravel or coarse sand. In the repairs I have seen making I saw no other preparation as foundation, but I am not sure that in first paving a street some greater and more elaborate preparation is not made. The French Ponts et Chaussées reports will doubtless give full details.

Sidewalks here are never paved with brick. There is generally a line of flags admitting of walking in single file; in the wider and more important streets two such lines. The rest of the sidewalk is either paved as the street, sometimes worse, i. e., with cobble-stones, which are torture to the feet, or else it is paved with small stones about the size used for concrete or macadamizing, which are laid in sand or gravel as close as they can be packed, points down and flat bases up, and then rammed to a smooth and even surface. These make a pavement easier to the foot than either flags or bricks, and as the stones are sorted and laid in patterns, far more pleasing to the eye than either. A space around every fountain or statue in the public places and streets of Berlin is paved with this mosaic. The colors used are red, gray, black, brown, which seem to be granites and sandstones, and white, which is of marble fragments.

In the pavement about the monument to Frederick the Great, the pieces of stone average two square inches surface each, or fifty of them fill a space of 10 by 10 inches. Below is one corner of this pavement:

Stars 10-rayed-white, with red centres. Color of pavement-red, gray, blue, white. This pavement never gets muddy like our gravel walks. It dries after a shower quickly, even more quickly than brick, and far more rapidly than flag-stone. A shower brings out the colors more vividly and improves its appearance. It is very pleasant to the foot and very ornamental to the street and squares. 35 w-Vol. ii

Your resources in Washington are red and gray sandstone from the Seneca quarries, brown from the stone-yards, blue limestone veined with white from the Potomac, gray granite, red fragments of brick, white spauls from the marble yards of the city, and doubtless other colors would be found if the attempt to introduce this pavement around the Greenough's Washington, the Jackson, the Mills's Washington, the fountain at the Capitol, &c., was made.

Shop-keepers in Berlin lay the whole pavement in front of their shops in this rude and cheap mosaic, sometimes. The name of the store or the number is sometimes introduced in block letters-white or black. The experience of these old towns leads them to pave the whole of their public squares which are not parks. They are used as market places-tables or wagons standing all over them. They are paved as the streets-nearly level-with very shallow undulations serving to carry off the water to the gully holes of sewers passing under them. The streets, which come in irregularly, seem to continue their pavement across on the direct lines of travel. The intermediate spaces are paved in irregular lines, or laid off into circles, triangles, &c., in which sometimes stones sorted of different tints are used with good ornamental effect, and sometimes the decoration depends upon the coursing above the block.

The space in front of such buildings as the Capitol is, in Europe-as far as I have yet seen-always paved. The court-yards of palaces are also paved like streets; not with flags or regularly cut stones, but with rough rectangular blocks like those used in Belgian pavements, and with mosaic of the small two-inch stone like Berlin trottoirs.

Rain and the broom keep all free from dust. The waste of gravel and sand east of the Capitol would be much improved by such a pavement; Belgian on all the lines much used by carriages-small mosaic on those parts used principally by footmen.

Asphalte is also much used for sidewalks in the German cities, as in Paris. With us it is too expensive, and I do not find it as pleasant to the foot as the small stone mosaic pavement, whose irregularity is sufficient to prevent the soreness caused by treading always upon a flat, hard stone surface, which presses the same parts of the sole at every step without any relief or change. My feet have been in a good condition to test the quality of pavement since I have been here, for since my sickness a little walking makes them very sore.

The Unter-den-Linden is a street of great celebrity in Berlin, and the people are still praising the electors who laid it out two hundred years ago. It is the principal street of a city of 600,000 people; upon it are the royal palaces, those of most of the princes, the principal shops and hotels. It has a wide gravel walk in its centre, four rows of trees which give shade, wide trottoirs or sidewalks next the houses, and yet it is never encumbered. The central walk is sometimes filled in the evening with promenaders enjoying the long summer twilight of this northern latitude, in which darkness does not come until 10 p. m. I give you a sketch of it, and I hope that Pennsylvania avenue may yet be arranged like it. It would, in our hot climate, be a great improvement, and the economy in paving it and keeping it in repair would be very great. In Berlin droschkies are the common carriages. They are large carriages, to open or close. The top lets down and they carry four to six persons, all behind one horse. The streets are very level and the pavements are excellent. I have seen a man and dog pulling many a four-wheeled wagon with as much furniture or truck on it as a good horse and cart draw with us. Dogs are in universal use by the street porters in place of horses-generally only one dog harnessed along a pole. The man or boy takes hold of the pole and pulls by a "bricole" over gutters; the dog does the whole work in smooth places.

But to the Unter-den-Linden, whose trees are not very large. They have, I suppose, perished in occupations of the city by hostile armies and been repeatedly renewed.

If the thirty-three feet carriage way happens to be full or obstructed, carriages take the twenty-four feet line between the trees, but these twenty-four feet lines are ordinarily used only by equestrians and by porters, who drag their wagons, assisted by their dogs. One of them, that on the north side of the promenade, is gravelled to be used as a summer road.

This street is the resort for business and recreation of all Berlin, and of all strangers.

Pennsylvania avenue is capable of a similar improvement. You see ninety feet are given exclusively to footmen, sixty-six feet to carriages, forty-eight feet are common property of footmen, horsemen, and carriages.

Hoping that these details will interest you, and serve, perhaps, as authority in introducing improvements as yet novel in Washington,

I am, with regards to our friends at the club, yours truly,

General MICHLER, Washington, D. C.

A true copy:

M. C. MEIGS.

N. MICHLER,

Major of Engineers, Bvt. Brig. Gen. U. S. A.

APPENDIX T-3.

Report of the engineer of the Washington aqueduct, appended to the annual report, dated October 1, 1867, of Brevet Brigadier General N. Michler, in charge of public buildings, grounds, and works.

OFFICE OF THE WASHINGTON AQUEDUCT, Washington, D. C., October 1, 1867. GENERAL: I have the honor to submit the annual report of the operations upon the Washington aqueduct during the past year, and an estimate of the amount required for its completion.

POTOMAC DAM.

At the date of the last annual report, October 1, 1866, work had been resumed on the Potomac dam at Great Falls, and it was confidently predicted that by the beginning of December the foundation masonry would be completed across the Maryland channel to Conn's island. A heavy freshet occurring on the 16th of October caused high water for the remainder of the season and a suspension of work upon the foundation masonry. The superstructure masonry was continued until December 20, when all operations were suspended for the winter.

This year the spring freshets were unusually high, accompanied by large masses of ice. Although the dam was unfinished, the masonry sustained very little damage. The water did not subside sufficiently until the 20th of June, when a large force of masons and laborers resumed operations, and although the season has been unusually wet and the work often interrupted by freshets, yet, owing to the energy and perseverance of the contractors, Messrs. Charles H. Sherrill and Anson Bangs, the foundation and superstructure masonry are now completed across the Maryland channel to Conn's island. A large portion of the temporary dam was washed away during the spring freshets, and several times during the summer. It was repaired after each freshet, and kept in repair until the present time.

GATEHOUSE AT GREAT FALLS.

The work on this gatehouse has been resumed, and it will be completed before he beginning of winter. The floor and the timbers supporting the iron gates

are very much decayed, and should be replaced with flooring and girders of cast-iron.

BRIDGES.

The stone bridges on the aqueduct are all unfinished.

An estimate of the

cost of completing them will be found at the end of this report, and also in each of the annual reports for the years 1864, 1865, and 1866.

The importance of completing these bridges cannot be overestimated. In their present state they are rapidly deteriorating, and if we have a succession of winters as cold and changeable as the last, their usefulness for aqueduct purposes will soon become seriously impaired.

CONNECTING CONDUIT AT THE RECEIVING RESERVOIR.

The work on the connecting conduit was resumed August 13, 1866, and vigorously prosecuted until its completion. Dalecarlia tunnel, eight hundred feet in length, was continued day and night until March 4th, when it was pierced through. On August 8th the waters of Powder Mill Branch and of the receiving reservoir were shut off, and the water of the Potomac (which since the 5th of December, 1863, had emptied into the receiving reservoir) was turned into the new connecting conduit.

In making the excavations for this conduit, more rock was encountered than was estimated for; nearly its entire length was built on rock foundations, but the most expensive and difficult portion of the work was Dalecarlia tunnel, a large part of which is constructed through soft and loose rock that is not selfsustaining. This part of the tunnel, as it progressed, was carefully shored with heavy timbers and every precaution used to protect the lives of the miners and to prevent the roof and sides from caving, yet extensive slides took place and several accidents happened to the workmen, though only one life was lost. Over one hundred feet of the south heading caved in and became an open cutting.

The cost of the connecting conduit has consequently exceeded the appropriation made by Congress in July, 1866, and there is a balance due the contractors, Messrs. Sherrill and Bangs.

Three hundred feet of the tunnel will have to be arched, and the water slopes of the embankment will have to be lined with ripraps to protect them from the waves of the receiving reservoir.

THE RECEIVING RESERVOIR.

On August 8th, when the Potomac water was turned into the connecting conduit, this reservoir was shut off from the conduit and has not been used since. The water in it, which had become very impure, was emptied out; it was refilled again and now contains about four days' supply, which can be used in the event of an accident happening to the conduit above.

This reservoir could be improved and made very useful for storage and settling of water, by deepening the shallow parts and lining the slopes with ripraps. Eventually this improvement will be found necessary. The lands in connection with this reservoir might be improved and beautified, and made into a park which would be easy of access and a desirable place of resort.

DISTRIBUTING RESERVOIR.

Work on the distributing reservoir was suspended in June, 1864. Since then it has been used for storage and settling purposes. On the completion of the connecting conduit, the Potomac water was introduced directly into this reservoir. Owing to its unfinished condition it is necessary to keep the water at a low elevation. When it is finished the water can be raised several feet higher,