If the axis of the valve terminates on the outside of the pipe in an elbow so as to form a crank, the strokes of the piston can be accelerated or retarded by turning this crank in one direction or the other. Suppose, for instance, that the crank must rise if the piston moves too fast, and should be retarded; and that it should descend, on the contrary, when the piston goes too slowly. By fitting a piece to the engine which must necessarily rise when the working is accellerated, and necessarily descend as soon as it is slackened, the problem would be solved, for it is only necessary to connect this piece in some way or other with the handle or crank of the valve. Such is the object of the contrivance which Watt called the governor. This apparatus is composed of an upright spindle which the engine turns more or less rapidly according to its own rate of working. Upon the upper end of this axis is fitted a horizontal pivot, to which two metallic rods are suspended by joints working freely, so that they may fly off, more or less, from the vertical. Each rod has a large metallic ball at the end. When the vertical axis is set in motion by the engine, the balls which turn with it fly apart to a certain limit, by the action of their centrifugal force. If the action of the piston becomes more rapid the balls fly farther apart, or approach nearer to each other in the opposite circumstances. In the first case the balls rise, and in the second descend. These rising and falling oscillations are communicated by levers to the handle of the revolving valve of the tube which supplies the steam, and any considerable alternation in the speed of the engine is in this way obviated. This apparatus, composed of movable rods with balls, this conical pendulum, as it was formerly called, had been long used as a regulator on the flour mills. It was also used to regulate the opening of flood gates of streams employed in setting overshot wheels in motion. This last application was precisely like, both as regards the end and the means, to that which watt made of it, in adapting it to the steam engine, in the year 1784.

[TO BE CONTINUED.]

Civil Engineering.

Description of Black Rock Tunnel, on the Philadelphia and Reading Railway.

By W. H. WILSON, Civil Engineer.

Black Rock Tunnel on the line of the Philadelphia and Reading Railway, is 1932 feet in length, 19 feet in width, and 17 feet in height. The form of the roof is a semi-ellipse of 19 feet base, and 6 feet height; the sides are perpendicular for five feet down, and then curved so as to give a width of 171 feet at bottom, or 18 feet on a level with the top of iron rail, which is 10 inches above the bottom. The floor is level throughout, and the area of the cross section is 301 square feet.

This tunnel was adopted to avoid the necessity of following a bend of the Schuylkill river, by which the distance would have been increased upwards of a mile and a half, and several abrupt curves made necessary. In order to facilitate the excavation, and afford a proper ventilation, six shafts were commenced, to be used both as working and air shafts; one of these was abandoned at the depth of 28 feet, in consequence of great interruption from water; the remaining five were excavated to the required depths. The depths to bottom of tunnel, are as follows: 116% ft., 139 ft., 1387o fr., 100% ft., and 821 ft., and the diameter of each is seven feet. Instead of being placed, as usual, over the centre of the tunnel, the shafts were located on one side, by which arrangement the difficulty of giving the proper direction for mining was somewhat increased, but the danger to workmen below from the accidental falling of bodies in the shafts considerably lessened.

The shafts were arranged in pairs (100 feet between each two) for the purpose of affording greater certainty in obtaining and preserving the proper direction of tunnel. The short space between two adjacent shafts being excavated first, two correct points were obtained in the centre line of tunnel, 100 feet apart, from the range of which the long drifts could be worked with accuracy. At first one gin was used for every two shafts, the bucket in each being alternately up and down, but as by this plan the material could not be taken away as fast as it was excavated, it became necessary to erect a separate gin for each shaft.

While sinking the shafts, common windlasses were used, worked by men, but when the drifts were commenced, the gins were put in operation. Each gin had two buckets attached to it, and was worked by two horses. The depth of open cutting at the North end of the tunnel is 47 feet, and at the South end 54 feet; the material as well as that removed from the tunnel and shafts was a very hard silicious slate rock. In sinking the shafts, it was found that but two men could work to advantage at the same time, one with a hammer, the other with a drill; this kind of work, laborious at any time, was made more so in this instance by the extreme wetness of the shafts, in consequence of which the tour of duty was limited to eight hours out of twenty-four, and in one of the shafts, for a short time, to six. At the top of each shaft two labourers were required to work the windlass and empty the buckets; these men were changed every twelve hours. The excavation of the tunnel was driven from both ends and from the five shafts, the area of the cross section being divided into two parts, of which the upper, comprising the arch, or roof, was excavated first, except in some few cases, where the peculiar stratification of the rock obliged the workmen to change their usual direction. At each end of the tunnel two separate bodies of workmen were constantly employed, one at the heading and the other some thirty or forty feet behind, completing the excavation to the full size.

In the drifts connected with the shafts, but one set of men could be worked to advantage, on account of the great difficulty in getting away the material. A set of men for one heading generally consisted of one superintendent and fourteen Miners, working seven drills; in addition to which, from two to five labourers were required to remove the material excavated. The time of labour was from six to six o'clock, deducting one hour at noon and at midnight, for meals, so that each man worked eleven hours out of twentyfour. Temporary railways were laid in each drift, upon which small cars with low wheels were used; the cars at the ends of the tunnel were larger than those in the other drifts, and so constructed as to tilt their burthens. At the shafts a bucket with a false bottom, secured by a hinge and bolt, was placed upon the car, then filled and rolled to the foot of the shaft, where it was attached to the rope; at the top, the bucket was hoisted sufficiently above the ground to admit of a car being run under it, when the bolt was knocked out, and the material fell into the car by which it was conveyed away.

The buckets used were two and a quarter feet in depth, two feet six inches in diameter at bottom, and two feet two inches at top, holding about nine cubic feet; those for raising water were about the same size, but made in a neater manner, with a valve in the bottom for letting off the water. The ropes used were one inch and a half in diameter, and passed around the large drum of the gin a sufficient number of times to prevent slipping; at each end was attached a hook with a spring to keep the bucket from getting off accidentally, and the length was such that one end would be at the top of the shaft while the other was at the bottom, From the time the shafts attained a depth of about 70 feet until the drifts leading from them became connected with each other, it was necessary to use some artificial mode of ventilation. Several different plans were tried, but the following was the most effectual; a wooden pipe about four inches square was secured to the side of the shaft by irons driven into the rock, and was attached at the upper end to a fanning machine; the wooden pipe was not allowed to reach quite to the spot where the miners were at work, as it would have been liable to injury from blasting, but the deficiency in length was supplied by a bag or pipe of canvass, which could easily be moved when necessary. The partial use of this machine was sufficient to supply a proper quantity of fresh air. This work, including the deep cuts at each end, and about seventeen hundred feet in length of grading adjacent to the south end, was contracted for by Mr. James Appleton on the 21st of October, 1835. In December the excavation of the shafts and deep cuts was commenced. On the 8th of March, 1836, tunnelling began at the North end, and in the course of the ensuing summer, drifts were successively started from the other points. The work was prosecuted night and day with very little intermission until completed; the number of men employed amounted at one period to about 450. The last junction of drifts was effected on July 7, 1857, and the excavation completed the same year. In July, 1838, the track on this division of the Railway was opened for public use. About 670 feet in length of the tunnel (heading) were worked from the ends, the remainder 1262 feet being excavated from the shafts. The following tables exhibit the progess made in excavating.

In the above tables, the second and third columns show the number of days and nights occupied in excavating the depth or length specified in the fifth column; the fourth column is an addition of the days and nights, showing the number of spaces of twelve hours each. It will be observed that the total of the fifth column in each table, does not correspond with the amount of work of the kind belonging to the tunnel; the balances not specified, were done at irregular times or with irregular forces, and would not consequently give a correct average. The following is the total cost of the tunnel and end cuttings:

The above includes work done and materials furnished of every description, no extra allowance being made for bailing water, use of machinery or any thing else. Among the items of expense incurred by the contractor, as stated by him are $6680 for powder, and $4372 for candles. The rock through which the tunnel is excavated is sufficiently solid to render unnecessary any support to the sides and roof, a cut stone façade at each end being all the masonry required. The hill at the north end of the tunnel rises very abruptly from the Schuylkill river, which is crossed by a neat stone bridge of four spans, situated on the same straight line with the tunnel. During the progress of the work several veins or seams were met with, containing calcareous spar, intermixed with sulphurets of iron and zinc, from which many beautiful specimens were taken. It was a source of much satisfaction to all concerned, that the junctions of the several drifts were effected without accident, and that the levels and lines of direction coincided exactly throughout the whole length. The above description has been compiled from a diary kept by the writer, who had the immediate management of the work, under the direction of Messrs. Moncure and Wirt Robinson, principal engineers of the Philadelphia and Reading Railway Company.

Eighth report of F. R. Hassler, as superintendent of the survey of the coast of the United States, and of the construction of standards of weights and measures; rendering account of the works of 1839.*

Upon the survey of the coast.

1. The proper organization and course of operation in a geodical work of such extent as the survey of the coast of the United States, is dictated by the nature of the country, and the relative position of its parts; presenting a long stretch of very unequal coast, with only such a breadth as the exigences of the work required; this dictated to begin at such an approximately central part of the country as would present the most facility and best prospects for large triangles, to serve as foundation of the work, and produce the greatest quantity of data for that purpose in the shortest time; presenting, also, within its limits, a locality for a base line of proportional length, and the necessary facility for its accurate measurement, from which the work might afterward spread in both directions of the country simultaneously, and alternately, as circumstances would dictate or allow.

2. Thence the work was begun in the neighborhood of New York Sound, Long Island, and its large sound, &c., which evidently present the requisites and qualifications above stated. The works of the preceding years had filled up with the main and secondary triangulation, and the topographical, as well as hydrographical detail, most part of the district from the Jersey shore of the Raritan and New York bay, till towards the east end of Long Island, the Sound, and opposite islands, the shore of the main land of New York, Connecticut, till Black Point, &c.

3. The field works of this last season were in some measure a beginning of the stepping over from the eastern side of these works to the southwestern, to open on that side, also, the field for the topographical and hydrographical detail works through the southern parts of New Jersey, part of Pennsylvania, to the seashore of Jersey, along Barnegat bay, and the Dela

ware.

4. All the survey of Long Island, as well the topographical, as the hydrographical part of its outer seashore on the south, and that of the sound to the north, had been completed the preceding years, till to Gardner's bay, of which a part of the sounding remained yet for this year.

5. The works of this year on the northern shore of the sound, include, as well the topographical, as the hydrographical surveys of Block island, the numerous islands of Fisher's sound, and others, the shore of Connecticut, and Rhode Island, with their deep inland waters, from Black point, where the hydrographical works had ended last year, through the whole of Fisher's sound, so that the work reaches now on that side of the shores and waters of the eastern States.

6. The surveys on land were carried inland as far as the nature of the coast on one side, and the time on the other, dictated or allowed; always furnishing, to the hydrographical party, which is carried on parallel with the works on the shore, the fundamental points to ground their determinations of the points of sounding upon them: these works occupied one of the sounding parties, and a number of topographical parties.

7. The other sounding party finished the works in Gardner's bay, thence * From Congressional Documents, 26th Congress-1st Session-read to the Senate December 27th, 1839.