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Threo rodmen did the regular rolling work and the fourth carried the plane table. Of the three regular rodmen the best man was selected as head rodman, the second best as side rodinan, and the less competent as rear rodman. The man showing the least aptness was detailed to carry the instruments.

The field platting was done in pencil and the sheets were executed in ink during rainy weather and evenings. These field sheets formed a complete record of the work, showing all fences, boundaries, shore line, waterways, dwellings, and all other topographical features of the ground, including, 20-foot contour lines. The notes, which contained only the data for finding the elevations of the contour points, were worked up at night by the recorder, and the elevations were then written on the field sheet. When sufficient area had been covered in this manner the contours were drawn. This method was found to be the most expedient when taking 20-foot contours on a scale of 1:10000.

It might be mentioned, however, that on very detailed work in mountainous country, where, say, 5-foot coutours may be required and the work is platted on a large scale, it would be best to change the above programme anıl compute the elevations with a slide rule while on the ground and draw the contours before leaving a station. This method is necessarily much slower, and though it was first adopted, it was soon abandoned and the notes were worked up in cainp.

A more detailed account of the manuer of doing plane-table work may not be out of place, and may be useful in future work on St. Mary's River.

The plane table was used much in the same manner as a transit in doing stadia work. A field sheet was commenced by locating upon it one of the lines of the tertiary triangulation system, for example, the course A A-AB, having previously decided upon the area of country to be covered by such a sheet, so that the line could be correctly drawn. This was usually done in camp. One of these stations, as A A, was then occupied, orienting the table on the line A-B, and shots drawn to all visible stations and prominent objects. The other station A B was then occupied with the iustrument oriented back on the line A-B, as before, and shots drawn to the same points as from the A A. This then located all the objects sighted, by intersection, assuming that the line A-B was correctly measured off on the field sheet. Such preliminary preparation forms a basis for checking all subsequent work on the sheet, and also affords means to locate the position of the instrument when placed at any point in the field.

The filling in of details on a sheet thus prepared was dono precisely as it would have been with the transit and stadia, only that each point was platted immediately in the field and all details were drawn before leaving the ground. It was made a practice to run polygonal lines between the points previously determined, thus checking both the original points, as determined by intersection, as also the polygon. In this way it was scarcely possible to introduce any error in the work.

The transit and stadia was used in the same manner as was done on the Mississippi River Commission survey, and the work was platted in camp and inked in the same manner as the plane-table sheets.

RECOMMENDATION REGARDING METHODS TO BE FOLLOWED IN FUTURE WORK. The comparative utility of the plane table and transit depends entirely upon the character of the topography and the weather.

The plane table can be advantageously used only in open country and during dry weather. Strong wind is a hindrance.

The transit can be used in any country and in any weather in which men can work.

In open country, where there is much detailed topographical work, I should say that a party could cover about the same area, in the same time, with either inst rument; but the plane-table work would be platted, while the transit work would not.

In woode:l country, or such localities where there would be comparatively few side shots, the transit has decided advantages, it being a much lighter instrument. especially a lapted to quick settings, and requiring no such care as is necessary to prevent the field sheet from becoming soiled or injureil.

As may be supposeil, my party was considerably delayerl between August 14 and October 12, the work being contined to weather which would not injure the planetable sheets. I have estimated a loss of about twelve days between the clates just mentioned, on which transit work coulil have been done porfectly well; but having no other instrument, this tine could not be utilized for field work, and the men were employed in the best possible manner preparing for future work. This time, therefore, was not an actual loss; yet the field work, which represented the real progress, was delayed.

This was the best part of the season, anl between October 12 and November 30, there were only fourteen days which would have permitted the use of a plane table, while with the transit only eight days were lost on account of severe rain and snow storms.

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It would seem, then, that a party ought certainly to be equipped with a transit, and, if practicable, to be provided with a plane table to be used when opportunities are offered. I should also recom

ommend, if new transits be purchased for future work, that these possess some of the features of the Buff & Berger plane table, that is, be provided with a telescope which can revolve on its optical axis, inaking the adjustment for collimation similar to that of a Y-level. The level should also be a detachable striding level as provided for the plane table. This will make the transit suitable even for running accurate levels.

The tangent screw for the horizontal movement of the plane table is a defective mechanism, for it produces a lost motion in the screw and the ball and socket joint. This movement should be carefully avoided in future instruments. The only perfect mechanism of this kind made up to this time is the movement which Messrs. Buff & Berger make for their transits.

It would be advantageous to have one or more of the stadia rods made to read 500 meters, instead of all to 400, as there is often great advantage in being able to read long station distances.

It might also be suggested that the rates of pay of the party be changed more in proportion to the duties imposed, and the following would seemn a fair disposition to make:

Per month. Recorder

$80 Head rodman

60 Two side rodmen

50 Rear rodman

$30 to 40 Cook......

30 to 50 As the progress of the work is greatly dependent upon the efficiency of the head rodman and recorder, these inen should be carefully selected and should possess a full knowledge of the work. The best men for this purpose aro young engineer students.

A fair knowledge of drawing is almost indispensable to the recorder, especially while doing plane-table work, as he is called upon at times to take the place of the chief, or do independent work when both transit and plane table are being used simultaneously.

If future work is to be done on a larger scale than last summer's, it might be advisable to provide two recorders, both of whom should be capable of doing instrumental wor... Such a party ought to be supplied with one rear and one head rodman in addition to the above personnel. Both instruinents might then be employed in the field and each used to its best advantage.

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STATISTICS.

Amount of work done. In attempting to state the amount of work done the only data which conveys a reasonable impression is the area covered, yet this is very unsatisfactory, as the amount of work necessary to survey a square mile of country ditters very widely. So, for instance, the vicinity of Sault Ste. Marie, Ontario, requires vastly more detailed work than does the open marsh meadow on Point aux Pins

During the season's work an area of 40 square miles was surveyed, containing a developed length of shore l ne of 38.7 miles. Of this area 17 square miles were surveyed with the plane table in 35.5 working days, and 23 square miles with the transit and stadia in 29 working days, making a rate of 0.48 square milo per day with the plane table and 0.65 sqnare mile per day with the transit.

The whole time spent in the field was 109 days, of which 35.5 + 29=64.5 days were spent in actual field work. The time lost to field work =109—61.5=14.5 days, is accounted for as follows:

Days. Sundays

16 Moving camp

6 Loss by ram while working with the plane table

14.5 Loss by rain and snow storms while using the transit.

8 Total...

44.5 ('ost of work. The following are the expenses incurred in equipping my party and burveying the above area on the Canadian shore of St. Marys River, between the Shingwauk Home and North Gros Cap, between the dates July 1 and December 1, 1893:

ENG 94_215

Instruments
Camp outfit
Provisions..
Labor, including chief of party.
Sundry expenses for traveling, etc

$305.00 302.38

369.29 1, 899, 98

85. 36

Total......

2, 962 01 Of the amount thus expended tho instruments and camp outfit are still available for future work. Assuming a depreciation in value of the instruments of 10 per cent and of the camp outfit of 50 per cent of the original cost, the following would represent the actual cost of the survey: Instruments, 10 per cent of $305.

$30.50 Camp outfit, 50 per cent of $302.38

151. 19 Provisions, labor, and sundry expenses.

2, 351, 63 Total....

2, 536. 32 This gives the average cost per square mile of survey,

$2,536.32

= $63.41, including

40 all expenses incidental to the work. Very respectfully, your obedient servant,

DAVID MOLITOR,

Assistant Engineer. First Lieut. CHARLES S. RICHÉ,

Corps of Engineers, U. S. A.

II.--REPORT OF MR. E. E. JIASKELL, ASSISTANT ENGINEER.

UNITED STATES ENGINEER OFFICE,

Sault Ste. Marie, Mich., April 28, 1894. Sir: I have the honor to submit the following report upon the reduction of the observations of tho line of precise levels run by Messrs. E. J. Thomas and A. 0. Wheeler in June, 1892, between B. M. “A” on the canal lock of 1881. at Sault Ste. Marie, and the water gauge at Waiska Bay.

In my last annual report (p. 4359 of the Report of the Chief of Engineers, U. S. A., for 1893) I made the statement that the elevation of the zero of the water gauge at Waiska Bay should be corrected by a minus 0.152 foot, the difference in the elevation of B. M. "F" and B. M. “A.” From the final computations of the levels it appears that Mr. Thomas must have had the elevation of B, M. “A” and called it B. M. “F,” so that there is no correction to the eluvation of the zero of the gauge at Waiska Bay as indicated in my report. B. M. “F” is the only one mentioned in the notes as the starting point for this line of levels, but the elevation of it or of the bench mark used does not appear, which accounts for my being led astray in my first interpretation of them.

In regard to the connection of this line of levels with the gauge at Waiska Bay we are dependent upon the statement made in the field report, which is undoubtedly correct, as to the elevation of its zero. In the notes there is no statement as to how the connection was made.

In connection with the reduction of the observations I havo determined the constants of the precise level, Kern No. 2, with which this line was run and these new values have been used in the computations. These values are given below:

Wire interval between extreme wires equals 1".038 for a base of 100+f+c where f=(m.366 and o=0m 177. Hence d, the distance, equals 96m.34 Stom.54 where 8 equals any intercept on the rod.

The value of one division of the level tube of tho stridling level was determined by means of a level trier, and found equal to 4".801.

The inequality of the collars was determined by the striding level with the result eye-end collar 0.53 of a division of the level tube, or 2.544 larger than object-end collar.

The observers were very careful indeed to make back and fore sights equal, so that in the whole line of 14 miles of double lino run there is only two or three stretches where any corrections appear. From my computations the zero of the Waiska Bay gauge is 1.1497 meters=3.7720 feet below B.M.“ A,” agreeing closely with the value given in the field report of the work.

There were four P. B. M.'s determined, located at intervals along the line, and the elevation of these, together with the descriptions of them, are given below:

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Elevation above mean sea level of B, M." A” on northwest wide wall of canal lock
of 1881=605.872 feet = 184.668 nieters.

Elevation of P. B. M. No. 1 above samo reference =642.007 feet = 195.682 meters.
Elevation of P. B. M. No. 2 abovo samo reference 611.312 feet = 195.470 meters,
Elevation of P. B. M. No. 3 above sa me reference = 670.321 feet 204.312 meters.
Elevation of P. B. M. No. 4 above samo reference - 648.027 feet = 197.517 meters.
Elevation of the zero of the Waiska Bay gauge 602.099 fect 183.518 meters.

.

*

DESCRIPTION OF BENCH MARKS.

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"P. B. M. No. 1 is tho top of a copper bolt set in the top of a large bowlder. The bowlder is 12 feet west from the center line of the Duluth, South Shore and Atlantic Railroad, and about 200 yards north of.tho 3-mile post, and is marked with the letters C.S. B. M., cut into the surface on the cast side.

“P. B. M. No. 2 is the top of a copper bolt in the center of a stone that is buried 4 feet decp. The stone is on the west sido of the Duluth, South Shore anıl Atlantic Railroad, 30 feet west from the center line of the track and 45 fcet north of the 6. mile post. A tamarac post, 6 inches in diameter, sets upon the stone, and projects abont 16 inches above the surface of the ground.

"P. B. M. No.3 is on the westside of the Duluth, South Shore and Atlantic Railroad, 21.5 feet north from tho I-milo post, and 31 feet west from center of railroad track. It is the top of a copper bolt set in a squaro stone that is buried about 4 feet deep. A cedar posterets on tho stone and projects 16 inches above surface of ground.

“P. B. M. No. 4 is the top of a copper bolt set in a stone that is about 18 inclics square and buried 4 feet in the ground. The stone is 344 feet north from the center line of the Duluth, South Shore and Atlantic Railroad, and 192 feet west from the west end of the railroad bridge across Waiska River, at Bay Mills station, almost due north from the frog on the branch line turning out to Waiska Bay. A cedar post 6 inches in diameter sets upon the stone and projects 2 feet above the ground. The letters U. S. B. M. are carved in the south side of the post."

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SLOPE OF THE RIVER.

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The Bay Mills gauge was read daily between 8 and 8:30 a. in. from June 6 to Sep, tember 9, 1892, inclusive. The elevation of the mean reading from this series of observations, or the mean lako level for this period, equals 601.826 feet above mean sea level. The gange at the head of the canal at Sault Ste. Marie is read daily at

The elevation of the mean reading for the period given above is 601.412 feet
abovo mean sea level, making the slope of the river from the Bay Mills gauge to the
head of the canal 0.414 feet, or 0.037 feet per mile, the distance between the two
gauges being in the most direct line by the channel 11.3 miles. This determination
of the slope for this reach is of course not as satisfactory as if the ganges had been
read simultaneously, but can be considered a close approximation.

In view of the excellent opportunities offered at Point Iroquois Light-House for
establishing a gauge and the possibility of having thelight-keeper read it daily for the
period of a year at least, I would respectfully recommend the continuing of this line
of precise levels from P. B. M. No.4 to Point Iroquois Light-House. This distance is
only 6 miles over a reasonably good road, representing not to exceed 4 days' work
for the ordinary leveling party. The angle party of the primary triangulation could
do this work at very small expense while they aro occupying A Troquois, which is in
the vicinity.
Very respectfully, your obedient servant,

E. E. HASKELL,

Assistant Engineer'.
First Lient. CHARLES S. Riché,

Corps of Engineers, U. S. Army.

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D D D 2.

REEXAMINATION OF ST. LAWRENCE RIVER.

REPORT OF CAPT. SMITH S. LEACH, ('ORPS OF ENGINEERS.

UNITED STATES ENGINEET: OFFICE,

Burlington, V't., July 1, 1891. GENERAL: I have the honor to transmit herewith my annual report on the reexamination of the St. Lawrence River under an allotment from the appropriation for survey of Northern and Northwestern Lakes, 1891. Very respectfully, your obedient servant,

SMITH S. LEACH,

Captain, Corps of Engineers. Brig. Gen. THOMAS L, CASEY,

Chief of Engineers, U. S. A.

An allotment of $4,275 was made May 2, 1893, and became available on July 1 following. It was based on the estimated cost of a resurvey of the main ship channel for a width of 2,000 feet from Lake Ontario to the foot of the Brockville Narrows, at Morristown, a distance of 40 miles.

Owing to the very uneven conformation of the bed of this part of the St. Lawrence the method of isolated soundings heretofore employed in all hydrographic surveys of a general character was inherently defective, and several shoals not disclosed by the original survey bad been reported. It was desired to examine the part of the channel used by deep-draft vessels under such conditions as to leave no possibility of points of rock which could be touched by vessels remaining undiscovered. It was decided to employ the method of continuous sweeping, for many years in use in verifying the removal of rock to certain spec. ified planes, but never before adapted to use on such a large scale. The apparatus devised and the method of working it are described in tbis report in a general way only, as the work remains unfinished and some details will be modified in future.

A decked scow, 60 by 15 feet, was anchored near mid-channel. Two anchors, one backing the other, were used, and in placing the scow the anchors were let go, the proper length of cable paid out, and the tug made fast alongside, head downstream, and worked at full throttle until the anchors held the strain without dragging. If they failed to hold, they were raised and thrown again a little to one side of their first position.

At the stern of the scow the end of a three-eighth-inch steel wire cable was made fast, and the cable was run out, with can buoys attached at intervals of 250 feet, until 2,750 feet were in the water. This part of the cable was called the permanent radius, and was the shortest line used until near the end of the season, when work was begun at 2,000 and finally at 1,700 feet from the scow. The last distance was found inconveniently short for a full sweep of 2,000 feet, but that or even less will do for narrow channels. At the lower end of this permanent radius a thimble was placed in the cable, and a second cable, called the vari. able radius, was made fast by a pair of sister hooks. The variable

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