'Tunnel of the Tavistock Canal, 155 



of direction which has been preserved in so long a drift, although 

 the junctions were made from several different points. 



Second, the small number of shafts, and consequently the length 

 of tunnel between each, which was ventilated during the progress 

 of the work. I am inclined to believe that it exceeds in this respect 

 all other attempts of a similar kind, and the section may therefore, 

 in the hands of the Geological Society, be a useful document for 

 future engineers. The means which I adopted for obtaining per- 

 fect ventilation will be found to be described in the Transactions of 

 the Society for the Encouragement of Arts, Manufactures, and 

 Commerce, for the year 1810. 



