already calculated in the first and third quadrant 

 of the circle of the second index. < >n the oilier hand, 

 they are to be added to the same in the second and 

 fourth quadrant, as is noted in their respective | 

 according to the theory of right ascensions. 



Here, then, [you have] as finally completed, 

 delineation of the great index which was partially 

 des« ribed I lefore in this book. 



I mm two points of that index which perpendicularly 

 correspond to the center of the^e circles, a pair of 

 compasses, by an unvaried aperture up to the circum- 

 ference o! the first larger circle, has marked oil lour 



- ii "i i i ii. le. The two larger segments, equal 



among themselves, in one aperture refer to the sun. 

 and the two smaller in the other, likewise equal, refer 

 to the moon. The one pointer is lor determining the 

 solar eclipses; the other, for lunar. Both segments of 

 division, like little wings of the index, stretch to 

 the extent of the degree of distance of the moon from 

 its nodes, and to which that determined latitude 

 corresponds. On one side, that latitude precisely 

 equals the radii of the earth, the sun. and the moon. 

 as the termini of solar eclipses; and, on the other side, 

 precisely equals the radii of the earth's shadow and 

 of the moon, as the confines of lunar eclipses. The 

 apexes of the last index, diametrically limited [op- 

 posite], indicate the age of the moon, and its mean 

 distance from the sun; one pointer, upon which the 

 sun sits, measuring the mean days and degrees from 

 the full moon: the other, on which the moon sits, 

 measuring the mean days and degrees from the new- 

 moon. 



a full star. Soon again, too slow to be observed, it 

 returns through the other half of the circle, so that 

 in the next conjunction, the whole face of the moon 

 may have a covering ol darkness, once again to be 

 removed. 



The other dials are moved by spontaneous ad\ 

 .H stated times. The tirst of these shows, through a 

 square opening, the day of the month: the second, 

 through another opening, shows the current day ol the 

 week with the characters Ol the seven planets which. 



ing to an< ienl supei stition, preside ovi i 

 day of the week i now . 1 1\ .1 truer form ol religion 

 divided by the Church into ferias, etc.); that is, the 

 sun. the moon, Mai Men ury, Jupiter, \ enu 

 Saturn, to which 1 have added the numbers of the 

 ferias. These two little dials are advanced daily, by a 

 sudden movement at midnight. The remaining three 

 are changed automatically only once a year on the 

 first of January. 



The first of these dials contains five little cells, 



opening from a common window: in the first cell, 

 at the edge of the dial, is found the dominical letter; 

 in the second, the cycle of the sun; in the third, the 

 character; in the fourth, the sign; and. in the fifth, 

 the house of the planet dominating the year. I In- 

 second dial shows the epacts, with the golden number. 

 The third, and last of all, shows the Roman cycle. 

 Finally, as indicated by the- epact and the dominie al 

 letter in an immovable table added outside, are the 

 iys ,ni<l other movable events of the year; that 

 is. Easter, the four seasons, the Rogation Days, etc. 



VI 



Besides the larger and smaller indices already men- 

 tioned, all [of which] revolve within the periphery of 



the three largest circles, six dials in this clock also 

 revoke within the same circles which are to be seen 

 through six openings of the frontispiece. I he first of 

 these, intended to indicate the phases of the moon by 

 an unusual method (completely black, and decorated 

 with the characters of the principal aspects of the 

 moon) continually revolves interiorly around the 

 center of the machine and .it the new moon, ii com- 

 pletely removes from sight the face of the moon 

 through the round window. It continually recedes 

 through the first half of the circle until, at the time 

 of the full moon, it restores the moon, looking out with 



VII 



But lest the various movements of the indices and 

 the various beginnings ol the divisions tend to cause 

 some fatigue, the precaution has been taken, that 

 all the indices by common law arc moved from the 

 top towards the right of the observer, and from thence 

 all the arithmetic divisions of the circles take their 

 beginning. And lest the multitude of different figures 

 should deceive the eve. the larger divisions of the 

 circles have been milked I >v Roman numbers, that 



is. by capital letters ol the alphabet; others, in other 

 places, by differently colored numbers. Thus, the 

 movements of the indices, the distribution of the 

 i in les and the multitude of numbers not only do not 

 disturb the eves and the mind, but rather marvelously 

 delight them. 



PAPER 35: THE BORGHESI ASTRONOMICAL CLOCK 



224 r.27—67 6 



73 



