The new imperial encyclopaedia, or, Dictionary of the sciences and arts : comprehending also the whole circle of miscellaneous literature ... . first: then the quadrantwill be adjusted for both methods of observation. To observe the Suns Attitude by thx-Back Observation. Re-move the coloured glasses toG, fig. 4, and look through the lowerhole in the sight-vane D, in the line of direction DN, directly lothe sun, and move the forward on (he arch exactly in thesame manner as in the fore observation : make the contact of thesuns limb and the back-horizon exact, and the degrees and mi-uutes
The new imperial encyclopaedia, or, Dictionary of the sciences and arts : comprehending also the whole circle of miscellaneous literature ... . first: then the quadrantwill be adjusted for both methods of observation. To observe the Suns Attitude by thx-Back Observation. Re-move the coloured glasses toG, fig. 4, and look through the lowerhole in the sight-vane D, in the line of direction DN, directly lothe sun, and move the forward on (he arch exactly in thesame manner as in the fore observation : make the contact of thesuns limb and the back-horizon exact, and the degrees and mi-uutes shewn by ihe index on the limb is the suns may be observed thatthe horizon will be inverted. If the sunslower limb be observed, the semi-diameter is lo be subtractedfrom the zenith-distance; but If the upper limb is observed, thesemi-diameter is to be added. The observation may i)e made inthe usual manner,- by turning the back ttv the sun. In tnis casethe coloured glasses are to be shifted to F, and proceed accoi-atngto the directions formerly given. Use of Hadleys Haadraat. The altitude of any object is de- tff miuetl. NAVIGATIOiN. Hie si<?\ane; otherwise, to the lower hole: and in t ms case, thenuadrant is to be held ^o thai the sun may be bisected by ihc lineol separation of the silvered and tniii;i)aieiit parts of the moon is lo be kept as nearly as possible in the same position;and the image of the star is to be observed .in_ the silvered part ofthe class adjacent to the line of separation of thetwo parts. I hereare two dilVercnt methods of taking observations with the <( In the first of these the face of the observer is du tcted to-wards that iiarl of tlic horizon immediately under the suii, and istherefore called the fore observation. In the other method theObservers back is to tliesnn, and it is hence called the back ob-servation. This last method of observation is to be used only%Vhen the horizon iindei llie sun is obscu
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