OF THE COUNTY OF TYRONE. 131 



In the feclrion, acrofs the pipe or gullet, the ftiape of 

 the road will appear thus, and give fome idea of the 

 quantity of water, that may be difcharged over it. 



"Roatl.a. 



The pipe is capable of difcharging fix cubical feet of 

 water, and the fegment, a, b t is equal to nearly ten 

 cubical feet. But there is no neceffity of being con- 

 fined to one pipe ; more may be introduced, if the cafe 

 fhould require it, and the excavation made in propor- 

 tion. Inflead of flags, logs of oak may be ufed, which 

 will laft for ages. 



SECT. 2. State of Navigations and Navigable Rivers. 



THE navigation from Strabane, for upwards of three 

 miles, where it falls in with the river Foyle, is cer- 

 tainly of infinite fervice to the county, on account of 

 cheapening the carriage of goods of various forts, from 

 ' K 2 Dcrry 



