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The same dial-plates1 cannot be used in all places, the shadow of the sun being sensibly different at distances of 300, or at most of 500 stadia2. Hence the shadow of the dial-pin, which is termed the gnomon, at noon and at the summer solstice, in Egypt, is a little more than half the length of the gnomon itself At the city of Rome it is only 1/9 less than the gnomon, at Ancona not more than 1/35 less, while in the part of Italy which is called Venetia, at the same hour, the shadow is equal to the length of the gnomon3.

1 "Vasa horoscopica." "Vasa horoscopica appellat horologia in plano descripta, horizonti ad libellam respondentia. Vasa dicuntur, quod area in qua lineæ ducebantur, labri interdum instar et conchæ erat, cujus in margine describebantur horæ. Horoscopa, ab ὥρα et σκοπέω, hoc est, ab inspiciendis horis." Hardouin, in Lemaire, i. 391.

2 These distances are respectively about 38 and 62 miles.

3 We are not to expect any great accuracy in these estimates, and we accordingly find, that our author, when referring to the subject in his 6th book, ch. 39, makes the shadow at Ancona 1/35 greater than the gnomon, while, in Venetia, which is more northerly, he says, as in the present chapter, that the shadow and the gnomon are equal in length. See the remarks of M. Alexandre in Lemaire, ut supra.

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