114 Mr Hepburn on the Obstructions in 



so (although undoubtedly original to Mr Hepburn), was point- 

 ed out (but not acted on) by Mr Hunter of Thurston, in a 

 letter to the Directors of the Edinburgh Water Company, in 

 January 1820. The circumstance of two persons having se^ 

 parately arrived at the same conclusion, marks strongly the ad- 

 vantages of the plan proposed. 



It may perhaps be unnecessary for the Committee to examine 

 minutely all the propositions in the esssgr, as to the air being 

 disengaged from being relieved from the pressure of the atmo- 

 sphere, and from the diminution of corpuscular attraction 

 (which is perhaps only a different term for the effect produced 

 by the former cause), but they consider the main fact of the 

 extrication of air in pipes satisfactorily elucidated. 



The self-acting apparatus would no doubt answer the pur* 

 pose intended, but probably in most cases the necessity for it 

 would not occur, as the letting off the air can be so easily done 

 by the hand, and being periodically required, could be done at 

 little or even no expense ; or, if an extraneous supply of water 

 at the highest point of the syphon could be obtained, some more 

 simple machinery might be made to effect the movement of the 

 valves. 



On the whole, the Committee are of opinion that the appro- 

 bation and thanks of the Society should be tendered to Mr 

 Hepburn for his ingenious contrivance of the double air-vessel, 

 and for his valuable essav. 



Copy Letter from James Hunter of Thurston^ to the Chairman of the 

 Water Company, Edinburgh, dated 20th January 1821, referred 

 to in the previous Report. With a Drawing* 



Sir, — I observe operations going on at the north end of the 

 Mound, Avhich I understand are the commencement of a tun- 

 nel upon a dead level below George Street to Queen Street, for 

 conveying the new supply of water to the lower parts of the 

 New Town. As this work (if I am correctly informed on the 

 subject) will cost a great sum of money, I think it ought to be 

 considered whether the following plan will not be a very great 

 saving. I should think George Street is not thirty feet higher 

 than Prince's Street, therefore, a syphon laid near the surface of 



.XX .JQV 



