Feb. 10, 1882.] 



♦ KNOWLEDGE 



317 



vl-., would be useful. Where else could tliey be so well 

 placed as at the points a, b, c, d, where the lines ir.s, w.n., 

 ■.»'., and f.n. intersect the diagonals of the square surface 

 of the pyramidal structure 1 Note, also, that these 

 observing stations would be at convenient distances from 

 each other. Tlie sides of this square surface would be 

 roughly about 1".") paces long, so that such a distance as 



Fig. 3.- 



-A Perspective View of the Upper Fonrth of the 

 Great Gallery. 



■i.ic, or a.O would only be about 62 yards (the length of 

 the Grand Gallery being about 5'2 yards). 



Thus there wruld be thirteen observer of azimuthal 

 directions and altitudes, whose work would be combined 

 with that of at least seven transit observers along different 

 parts of the length of the Great Gallery with its seven 

 transit widths (as shown by its section, Fig. 2). Twenty 



observers in all, the transit workers, provided with the 

 great fixed transit instruments in the Gallery itself, the 

 others armed, perhaps, with astrolabes, armillary spheres 

 for reference, direction tubes (or ring- -arrying rods) would 

 be able to make observations only inferior in accuracy to 

 those made in our own time with telescopic adjuncts. 



Fig. 3 is intended to show something of the structure 

 of the interior of the Great Gallery. Tlie stones outside 

 are supposed to be seen in section, only one-fourth of the 

 Gallery being given. For correct perspective, six or seven 

 more layers of stone should have been shown below the 

 lowest in the picture. But this would have given to the 

 illustration an inconvenient shape. It will be seen that 

 a section of the southern sky, very convenient for ob- 

 ser\ ation, would be seen from the interior of the Grand 

 Gallery. The central vertical through this section would 

 (as seen from the middle of any of the cross seats) be the 

 true meridian. But the moment of transit might be 

 equally well observed by taking tlic moments when a star 

 was tirst seen (from the middle of a cross seat) on the 

 eastern edge of the vertical sky space, and when the star 

 disappeared : the instant midway between these would be 

 the true time of transit. B}' combining the observations 

 made by several "watchmen of the night," stationed in 

 tlifferent parts of the Grand ( Jallery, a very close approxi- 

 mation to true sidereal time could be obtained. 



1 apprehend, however, that astronomers who had shown 

 themselves so ingenious in other respects, would not have 

 omitted to note the advantage of suitably-adjusted screens 

 for special transit observations : and it seems to me likely 

 that the long grooves shown in section at /i and k', Fig. 2, 

 might have been used in connection with such a purpose, 

 and not merely (though that was probably one of the 

 objects they were intended to subserve) to carry a hori- 

 zontal sliding cross-bar, by means of which the altitude 

 of a celestial body at the moment of transit could 

 be more readily determined. We must not forget 

 that transit observers have to determine what is called 

 the declination of a star (its distance from the 

 equator), as well as what is called the right ascension, 

 or distance measured parallel to the equator from a certain 

 assigned point on that circle. For this purpose the hori- 

 zontal lines a a', b b', itc, (F'ig. 2) would be useful, but not 

 sufficient. I incline to think that the method used to 

 obtain accuracy in observations for determining declina- 

 tion involved a very practical use of the grooves k k' . 

 Possibly a horizontal bar ran from k to k', carrying vertical 

 rods, across which, at suitable distances, horizontal lines 

 wf-re drawn (or, better still, horizontal rods could be slid 

 to any required height). The horizontal bar could be slid 

 to any convenient position, the vertical rods adjusted, and 

 at the time of transit the horizontal rods could be shifted 

 to such a height as just to touch a star as seen by an ob- 

 server in the Gallery atthe moment of mid-transit 



If a telescopist in our own time will try to plan out a 

 method of determining the declinations and right ascen- 

 sions of stars (say, for the purpose of forming a trust- 

 worthy star chart or catalogue), w ithout using a telescope, 

 by using such an observing place^as the Great Gallery, he 

 will .see how much might be done, so far as equatorial and 

 zodiacal stars were concerned ; and they are altogether the 

 most important, even now, and were still more so in the 

 days when the stars in their courses were supposed to rule 

 the fates of men and nations. 



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