This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1885 Excerpt: ... at time T; 6T = hourly rate of clock. The Azimuth Constant, a. 186. This can only be determined by observation of stars. Let two stars be observed which differ as widely as possible in declination. Let 7" and T' be the times of observation reduced to the middle (or mean) thread; 6 and the declinations of the stars; a ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1885 Excerpt: ... at time T; 6T = hourly rate of clock. The Azimuth Constant, a. 186. This can only be determined by observation of stars. Let two stars be observed which differ as widely as possible in declination. Let 7" and T' be the times of observation reduced to the middle (or mean) thread; 6 and the declinations of the stars; a and their right ascensions. Then equations (304) will apply to these stars, except that in the second we shall have a' and 8' in place of a and tf, and the sign of c is not changed. Let us write t = T-f 6T(T-T) + b cos (p-6) sec 6 + c sec 6--."021 cos p sec 6; t' = T + 8TT-T, ) + cos-tf') sec c sec d'--"-021 cos p sec tf'. That is, we plr.ce / and t' equal to the sum of the known quantities in the second members of the equations. Equations (304) then become a = t 4-A T, 4-- sin (9--) sec; at = f + AT + a sin (9-8') sec From which (rt'-a)-(f-()--sin (p--8') sec 8'--sin (p--rf) sec ' ' which reduces to a = (-'--o-y-0, .07) cos p (tan 8--tan tf')i 7) The greater the denominator of this fraction the smaller will be the effect upon a of errors of observation. If two circumpolar stars are observed, one at upper and one at lower culmination, the denominator of 307 becomes cos p tan 8--tan (1800--tf') = cos p (tan 4-tan 8'). This combination is therefore most favorable for the purpose. If the rate of the clock and the stability of the instrument can be relied on for twelve hours, the same star may be observed both at upper and lower culmination. This will not be practicable, however, with a portable instrument. If two stars are observed at upper culmination, one should be near the pole and the other near the equator. If 111 and n are required, they may now be computed by (276), or we may proceed as follows. 187. Using the ...
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