VOL. LXXVIII.] PHILOSOPHICAL TRANSACTIONS. 511 



attending a date, to be ascertained, at a distant period of time, from the phase 

 of the moon, which is retarded or advanced by so complicated a variety of cir- 

 cumstances: and the ambiguity appears, in the 2d place, to have been 

 promoted by the custom of the Arabs beginning their day at sun-set; conform- 

 ably with which idea, the time when the moon became visible at Mecca, being 

 the evening of Thursday the 15th, according to our mode of computation, was 

 to them the commencement of Friday; which Friday, beginning a few hours 

 later, we term the l6th of July. At that period the cycle of the sun was 15; 

 the cycle of the moon, or golden number, 15; the Roman indiction 10; and 

 the dominical letter c. 



The year of the Mahometans consists of 12 lunar months, and no embolism 

 being employed to adjust it to the solar period (as practised by the Chaldaeans and 

 Hebrews, who were in other particulars their guides, and anciently, it is said, 

 by the Arabs themselves), the commencement of each successive lunar year 

 anticipates the completion of the solar, and revolves through all its seasons, the 

 months respectively preserving no correspondence. In order to form a just and 

 accurate idea of the length of this year, and of its component months, it will be 

 necessary to distinguish 2 modes of estimating their commencement and dura- 

 tion. These, though their difference is not progressive, never amounting to 

 more than 2 whole days, and rarely to so much as 1, may yet, if misunder- 

 stood, occasion in some instances, uncertainty and error : and more especially as 

 the writers on this subject have inadvertently fallen into contradictions, from 

 neglecting to explain to their readers a distinction of which they must have been 

 themselves sufficiently aware. These modes may be denominated the vulgar or 

 practical, and the political or chronological reckoning. 



The vulgar or practical reckoning is that which estimates the commencement 

 of the year, or first day of the month Moharram, from the appearance of the 

 new moon, on the evening of the 1st or 2d day after the conjunction, or from 

 that time at which it might from its age be visible, if not obscured by the cir- 

 cumstances of the weather, which is scarcely ever so soon as 24 hours, and 

 seldom later than 48 hours, after the actual change. This appearance is 

 announced by persons placed on the pinnacles of the mosques or other elevated 

 situations, to the people below, who welcome it with the sound of instruments, 

 firing of guns, and other demonstrations of respect and zeal. The month thus 

 commenced is computed to last till the new moon again becomes visible; and so 

 of the remaining months, till she has completed her 12th lunation, and, emerg- 

 ing from the sun's rays, marks the practical commencement of another year. 



In the political or chronological mode of reckoning, the return of a new 

 year, or the duration of the months which compose it, is not regulated either 



