VOL. LXXVIII.] PHILOSOPHICAL TBANSACTIONS. 50Q 



20 and 21, grow much faster than any of the rest, but are neither of them 

 handsome growing trees. N° 20 has several seams where the bark is parting 

 ' from the wood, and are likely to be dead sides. N° 2 1 was about as thick as a 

 walking-stick in 1730. It does not grow round and smooth, has no dead side, 

 but several deep furrows in it, so that these 2 trees seem to grow faster than they 

 can grow well. In 1733, N° 23 was about as thick as a pitch-fork shaft. The 

 elm N° 37 was planted with the quick in January, 1756, and cut down to the 

 ground as that was. It is a kind of wifch elm, which grow faster than the up- 

 right ones, and with large round heads. N° 38 is so far like a witch elm, that 

 at 10 feet high it parts into a great head; but it grows much straighter and 

 handsomer than that kind of tree generally does. 



Planted trees at a distance from the hedge seem not to grow so large as sown 

 trees in the hedge; whether from the check the roots receive in transplanting, 

 or that the trees not in hedges are more rubbed by the cattle; perhaps both 

 causes concur when the trees are transplanted large; but trees set in quicks, 

 when very small, do not seem to be hurt by it. Mr. B. had some oaks set with 

 the quick, and a row of acorns was some years after sown against it; but in be- 

 tween 40 and 50 years they have not overtaken the planted ones in size; the 

 sown seem however inclined to be taller trees than the planted. 



XXV^III. On the Era of the Mahometans^ called the Hejera*. By William 

 Marsden, Esq., F.R.S.^ and A. S. p. 414. 



In their computation of time, the Arabs, and other Mahometan nations, 

 reckon by a year which is purely lunar. It has no reference to the solar revolu- 

 tions, and is of course unconnected with the vicissitude of seasons. The pur- 

 pose of its adoption appears to have been chiefly religious, for the regulation of 

 fasts and ceremonies, rather than that of the civil concerns of the people. 

 Perhaps a conscious ignorance in matters of science might have determined the 

 institutors to prefer a period whose limits were marked and obvious to the senses, 

 to one whose superior accuracy depended on astronomical calculation; and it 

 may also be conjectured, that their habits of life rendered the adjustment of the 

 tropical year less interesting to these turbulent and wandering fanatics, than to 

 nations whose attention was directed to agriculture and other peaceful arts. 



The era of the Mahometans, called by them the Hejer^, or Departure, is 

 accounted from the year of the flight of Mahomet, their prophet, from Mecca, 

 in Arabia Petrasa, to Medina, at that time called Yatreb, which was the 13 th 

 of his pretended mission, the year of Christ 622, and of the Julian period 

 5335. This event, but little memorable in itself, and deriving no celebrity from 



* As this mode of spelling the word differs from that commonly followed, it may be proper to 

 observe, that the Arabic letters of which it is composed are h, j, x, a, or ah, and that tlie supplied 

 vowels are to be pronounced short — Orig. 



