411. Contouring. (Fig. 70a.)

Three points forming the vertixes of a triangle, A B C, whose altitudes above the sea, or datum line, are given. Lines are chained from A to B, B to C, and C to A, and stations marked at given distances, and contour points made at every change of altitude equal to 10, 20, or 30 feet. Lines are chained down the side of the hill, and connected with checklines. The level of station a is carried around the hill, showing where the contour line intersects each chain line, to the place of beginning. Begin again at the next station, b, below, and proceed as in the above, and so to the lowest station. The contour lines will be the same as if water raised to different heights around the hill, leaving flood-line marks on the hill. The plotting is similar to triangular surveying.

of the hill requires practice.

The shading

Final Examination. When a plan is ready for final examination, tracings are taken, of such size as to cover a sheet of letter paper, or white card-board of that size, made to fit an ordinary portfolio. In the field, the examiner puts himself in the direction of two objects, such as fences or houses, and paces the distance to the nearest fixed corner, and, by applying his scale, he can find if it is correct; by these means he will detect all omissions and errors. He will be able to put on the topography of the survey. He generally finds pacing near enough to discover errors, but where errors occur, he chains the required distances.

412. In plotting in detail we use two scales, one flat, 12 inches long, but having the same scale on both sides, such as one chain to an inch, or three chains to an inch. The other scale is 2 inches long, for plotting the offsets graduated on both sides of the index in the middle, ends not beveled. If the index is one inch from each end, we draw a line parallel to the chain line, one inch distant. If the index is two inches,

we draw it two inches from the line. On each end of the small scale we have, at two chains' distance, lines marked on it to check the reading on the large scale. At each end of the chain line, perpendiculars are drawn to find the point of beginning. The large scale in position, the small one slides along its edge to the respective distances where the offset can be set off on either side of the chain line.

413. Finishing the Plans or Map.

Indian ink, made fresh, to which add a little Prussian blue, expose to the sun or heat for a short time, to increase its blackness.

1 and 2. FORESTS AND WOODS.-Jaunne jonquille, composed of gum gamboge, 8 parts; Prussian blue, 3 parts; water, 8 parts. The woods have not the trees sketched as heavily as forests.

3. BRAMBLES, BRIARS, BRUSHWOOD.

by adding 4 parts of water.

Same as No. 1, but lighter,

4. TURF-PIT.--The water pits by Prussian blue, and the bog by sepia and blue.

5. MEADOWS OR PRAIRIES.-Prussian blue, 6 parts; gamboge, 2 parts; and water, 8 parts.

6. SWAMP. — In addition to dashes of water, we pass a light tint of

Prussian blue.

7. CULTIVATED LAND.-Sepia, 6 parts; carmine, 1 part; gamboge, 1⁄2 part.

8.

CULTIVATED LAND, BUT WET.-Same as above, except that dashes of water are marked with blue.

9.

10.

TREES. -Same as 1 and 2; sketched on, and shaded with sepia.
HEATH, FURZE.- Une teinte panachée, nearly green, and light

carmine.

Teinte panachée is where two colors are taken in two brushes, and laid on carefully, coupled together.

11. MARSII. The blue of water, with horizontal spots of grass green, or to No. 5 add 2 parts of water.

12.

13.

14.

15.

16.

PASTURES.-To No. 5 add 4 parts of water.

VINEYARDS.—Carmine and Prussian blue in equal parts.
ORCHARDS.--Prussian blue and gamboge in equal parts.

UNCULTIVATED LAND, FILLED WITH WEEDS.-Same as No. 3. FIELDS OR ENCLOSURES.-Walled in are traced in carmine, and if boarded, in sepia. Hedges, same as for forests, to which is added 2 parts of green meadow.

17. HABITATIONS. -A fine, pale tint of carmine, light, for massive buildings, and heavier for house of less importance.

18. VEGETABLE GARDENS.—Each ridge or square receives a different color of carmine, sepia, gamboge-the color for woods and meadows.

19. PLEASURE GARDENS, FLOWER GARDENS. Are colored with meadow color, and wood color for massive trees; the alley, or walks, are white, or gamboge with a small point of carmine.

20. The colors used are, generally, Indian Ink, Carmine, Gamboge, Prussian Blue, Sepia, Minum, Vermillion, Emerald Green, Cobalt Blue, Indian Yellow.

This method of keeping a field-book was used by the English and Irish Board of Works. Size of books 8 by 64 inches.

Many Engineers there kept their books thus: ruled from left to right, Back Sights, Fore Sights, Rise, Fall, Reduced Level, Distance, Permanent Reduced Levels, and Remarks. Book, 71⁄2 by 5 inches.

414a. Colonel Frome, Royal English Engineer, in his Treatise on Surveying, gives, from left to right, Distances, B. S., F. S., +, Rise, Fall, Remarks. The columns Rise and Fall show the elevation at any station above datum, that assumed at the beginning.

Sir John McNeill's plan of showing the route for the road, and a profile of the cutting and filling on the same: the line is not less than a scale of 4 inches to 1 mile, and the vertical sections not less than 100 leet to an inch.

415.

Our Method.

=

B. M. + Back sights + 50.0 10. + 8. + 6.50 = 74.50 F. sights at turning points 11.50 + 18.00 + 7.00

36.50

Proof,

38.00

416. Levelling by Barometrical Observations.

BAROMETRICAL MEASUREMENT OF HEIGHTS.

TABLE A.

THERMOMETERS IN OPEN AIR.

BAILY.

A

A

4.74914

109

4.80183 145 4.81807 | |

966

544 110

851

4.75017

895

069

172 42

223 43

939

3

983

412 | 150 | 4.82027

071

6

12

479 48

844.79019 | 120

364.76692 72 4.78449 108 4.80137 | 144 |

NOTE. t temperature of the air at the lower station; t' = that at the upper station; A correction for temperature, dependent on t + t'. And for Table B.: r = temperature of mercury at the lower station; I' that at the upper station; B correction due to the mercury dependent on r r; C correction for the latitude of the place; D latitude; R height of barometer at lower station; R' = height_of_barometer at upper station.

These Tables are from the Smithsonian Meteorological and Physical Tables, published in Washington, 1858.

In 1844, in Ottawa, Canada, Mrs. McDermott, in my absence, kept a record of numerous observations of the state of thermometer and mountain barometer, for Sir William Logan, Provincial Geologist, then making a tour of the valley of the River Ottawa and its tributaries. (See his Geological Reports.) The observations were made at the hours of 7, 9, noon, 3, and 6, to be used for the lower Station, at Montreal.