Engineers' Surveying Instruments by Ira Osborn Baker

Author:Ira Osborn Baker
Language: eng
Format: epub
Publisher: J. Wiley & sons
Published: 1892-03-25T05:00:00+00:00

For valuesQof Q on this page ]

t-f/) CM S > 0.95(^4-/) ^ (<*+/)

(fi 4-y) szH Q varies between o.3(t -f/") and a3(c +/>

ART. l]

THE STADIA.

199

For«toe»<rf90H this page{(^^^^,g ,,g^ ^^^ ^^^^^ ^^^^^

given by the scale at the left of the diagram is the value of ks sin* 6^ which is to be subtracted from ks. For extreme accuracy add (<r+/). For example, if ks = 740 and 6 = 10°, what is ZT? On the bottom line find 740, and follow the inclined line to an intersection with the radial line marked 10°. By the scale on the left this point reads 22.4. Therefore -Z?= 740—22.4 +

If 6^ is more than 13°, the method of using the diagram differs slightly from that just described. For example, if ks = 820 and fl= 17°, what is HI On the extreme right-hand line of the diagram, find 820 and follow this horizontal line to its intersection with the radial line marked 17**, and then follow this oblique line to the scale at the top, we see the value sought is 70. Therefore H = 820 — 70 + (^ +/)•

227. Vertical Distance. Fig. 58 (between pages 200 and 201) gives the value of ^kssinzO (see equation

(i3)» page 194).

This diagram is used in essentially the same manner as Fig. 57 (§ 226). If the observed value of 6 is found in the left-hand triangle or section of the diagram, the value of ks is to be found on the bottom line to the left of the center, and the final result is found on the left edge of the left-hand triangle. If the value of d is found in the middle section, the value oi ks may be found as before, then following the inclined line up to the 6° line, and from this point following a horizontal line to the radial line corresponding to ^, and from thence following the oblique line to the scale on the upper edge of the drawing, find the value sought ; or if preferred, the value of ^x and also of the final result may be found by the numbers written upon the face of the diagram. If the given value of 0 is found in the right-hand triangle or section of the diagram, find the value of ^5 on the bottom line to the right ot the center, and

follow the more inclined lines to the intersection with the proper radial line; and then the reading of this point by the scale of the nearly vertical lines is the value of i kssin 2 6, Fig. 58 was constructed very carefully, and can be used with confidence ; and ordinarily will give results as accurate as the observations.

Concerning the term {c +/) ^^^ ^ of equation (13), page 194, notice that it is always small, and varies but slightly for a considerable change in 6 ; and therefore the supplemental table on Fig. 58 gives this term with sufficient precision. The first two values of {c-\-f) in this table are to be used when the metre is the unit, and the last two when the foot is the unit.

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