Water-pipes and Syphons from disengaged Air, ^c. 101 



the air was to be expelled by a powerful force-pump. The double 

 air-vessel, which I had previously projected, appearing to me 

 much more effective, as well as more simple and economical, it 

 occurred to me to submit a description of it to the Directors of 

 the Highland Society, who were pleased to honour it with their 

 thanks, and a place in their Transactions. It was not till very 

 lately that I had a model constructed, — the operation of which, 

 while it confirmed my opinion of its practical utility, suggested 

 some improvements on the design. The present paper contains 

 the statement of the result, particularly as applied to water-pipes, 

 and especially to the means of obtaining the command of water 

 lying beyond a ridge of high land. My chief reason for sub- 

 mitting it to the Society of Arts is, the belief that the approba- 

 tion of so competent judges (should it appear to deserve it), 

 would be the best means of obtaining for it a trial in practice. 

 Although the application of an air-vessel is not, as I at first sup- 

 posed, altogether new, this particular mode of its application, 

 and the deduction of the causes of obstruction of pipes by air, I 

 believe to be so, at least I am unable to learn any thing to the 

 contrary. 



I shall be obliged by your recommending the paper to the 

 notice of the Directors. And I have the honour to be, &c. 



J. Stewaet Hepburn. 



James Tod, Esq. W. S. 

 Secretary to the Society of Arts of Scotland. 



It has been long known that all fluids, exposed to the ordinary 

 pressure of the atmosphere, absorb a portion of the air, which, 

 however, appears to be rather mechanically diffused through the 

 fluid than chemically combined with it, being retained in union 

 with it by a force which is in the conjunct ratio of the atmo- 

 spherical pressure and the corpuscular attraction of its particles. 

 Accordingly, the quantity of air which any fluid is capable of 

 holding in solution, varies with the degree of pressure to which 

 it is subjected, and with the varying state of its corpuscular at- 

 traction. Of the effect of increased pressure in augmenting the 

 capacity of fluids to hold gases in solution, a familiar instance 

 occurs in the case of aerated waters, and of liquors which have 

 been bottled up before the termination of the vinous fermeuta- 



