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{hew that a bridge fr&m 2 to 300 feet fpan may be 

 conflruded at lefs than half the expence that the 

 price of driving the materials only for an ordinary 

 bridge in mofl: cafes would coft. The power of 

 lengthening the fpan, fo as to avoid the neceffiiy of 

 central piers, is in fome fituations, efpecially where 

 rapid torrents occur, or great heights are to be le- 

 velled, of prodigious importance. 



In the beginning of lafh fummer I publiflied a fmall 

 Treatife on Peat-Mofs, a copy of which I have defired 

 my bookfeller in London to deliver to your order, 

 together with a Treatife on Sheep by Dr. Pallas, 

 m which you will find fome obfervations of a fimilar 

 nature to thofe in the paper fent, with fuller illuftra- 

 tions on fome heads ; though -it is placed in a very 

 different point of view in fome refpefts. 



In the Treatife on Mofs, to adopt a fafliionable 

 phrafe, you will find that I have /ported a new opi- 

 nion refpe£ling the theory of its formation, which I 

 find proves very hard of digeftion to the naturalifts 

 of the prefent day. After having fliewn, by fafts 

 that cannot be controverted, that mofs could not 

 " have been produced in the manner that has been 

 commonly received as inconteftibly certain till jufl 

 now ; I put it as a query, whether peat-mofs is not 

 a living plant, and not a congeries of decayed plants 

 in a particular Hate of prefervation, and give reafons 

 for fufpecling that it may be fo. I have not found 



as 



