Place the index A at the apparent distance on the arc of the instru-
ment ; then place the plain bar BC on the divided edge BE,
or solar line.) at the sun's altitude ; and the chamfered bar DF,
on the lunar line GH : mark at what division the plain bar intersects
it, which note down, and call it the line of correction ; and when this
falls to the right of the lunar line, it is subtractive ; but when to the
left, it is additive.
Multiply* this line of correction by the given horizontal parallax ;
and divide the product by 62, when the correction is subtractive ; but
by 53, when additive, to find the " true correction."
To this description I will add a comparative example by the two
methods.
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By the usual Formula. p's Apparent Altitude, 32° 30' 00"" ,,. *'s Ditto ditto,.. 43 43 00 Glven > i Apparent distance, 45 19 37 To find the true d 1S tance. |_ ]) 's Horizontal Parallax, 60 09 3) 's Apparent Altitude,32 6 30'
- 's Ditto ditto, 43 43
Sum 76 13 Half, 38 6 Co. Tang. 10,1056 Difference, 11 13 Half, 5 36 Tangent, 8,9915 Apparent distance, 45 19 37 Half, 22 40 Co. Tang. 10,3792 First Correction, .. + 6 Arc, A. .. 16 40 Tangent, 9,4763 45 19 43 Difference, s 6 00 Co. Tang. 10,9784 Second Correction, — 25 43 *'s Altitude, 43 43 Co. Tang. 10,0195 44 54 00 *'s Correction, 59 P. Log. 2,2626 Third Correction, + 15 First Cor. 6 P. Log. 3,2605 True Distance, .. 44 54 15 Sum, 39 20 Co. Tang. 10,0865 }) 's Altitude, 32 30 Co. Tang. 10,1958 J'sCor 49 15 P. Log. 0,5629 2nd Cor 25 43 P. Log. 0,8452 Given as above. By the Anglometer. Line of Correction, 25' 45" P. Log. 8445 J 's Horizontal Parallax, 60 9 P. Log. 4760 1,3205 Constant Log. 4629 8576 Correction, 24 59 Apparent Distance, 45 19 37 True Distance, 44 54 38
- The use of proportional logarithms will simplify this operation.
