A primary astronomy .. . dried with heat,f Frig-id, cold, wanting heat or warmth. PRIMARY ASTRONOMY. m 109. What is the greatest Longitude that any place can have ?One hundred and eighty degrees (180°). 110. What is meant by the Sensible Horizon 1 It is that circle which terminates our view, or wherethe earth and sky seem to meet. 111. What is the Rational Horizon ? It is an imaginary plane, below the visible horizonand parallel to it, which, passing through the earthscenter, divides it into upper and lower hemispheres. [1. These hemispheres are distinguished as upperand lower with reference t
A primary astronomy .. . dried with heat,f Frig-id, cold, wanting heat or warmth. PRIMARY ASTRONOMY. m 109. What is the greatest Longitude that any place can have ?One hundred and eighty degrees (180°). 110. What is meant by the Sensible Horizon 1 It is that circle which terminates our view, or wherethe earth and sky seem to meet. 111. What is the Rational Horizon ? It is an imaginary plane, below the visible horizonand parallel to it, which, passing through the earthscenter, divides it into upper and lower hemispheres. [1. These hemispheres are distinguished as upperand lower with reference to the observer only. 2. The sensible horizon is half the diameter of theearth, or about 4000 miles from the rational: andyet so distant are the stars that both these planesseem to cut the celestial arch at the same point;and we see the same hemisphere of stars above thesensible horizon of any place that we shoidd if theupper half of the earth were removed, and we stoodon the rational horizon of that place.] -&-H0RI. 112. What are the Zenith and Nadir Points ?The Zenith is the point directly overhead, and theNadir the point directly under our feet. [1. These directions, it must be remembered, are merely relative. As the earth is asphere, inhabited on all sides, the Zenith point is merely opposite its center, and theNadir toward its center. So with the directions Up and Down : one is from thecenter, and the other toward it; and the same direction which is up to one is down toanother. This fact should not merely be acknowledged, but should be dwelt uponuntil the mind has become familiarized to the conception of it, and divested, as faras possible, of the notion of an absolute up and down in space. We should remem-ber that we are bound to the earths surface byattraction, as so many needles would be bound tothe surface of a spherical loadstone. 2. East and West also are not absolute, butmerely relative directions. East is that directionin which the sun appears to rise, and West ist
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectastronomy, bookyear18
