694 PHILOSOPHICAL TRANSACTIONS. [aNNO J 755, 



Letter 3, from Mr. Walter Taylor, dated Woolwich Yard, Feb. 25, 1756. p. 526. 



The tides the last week, and even for some days this week, have been very 

 irregular and unusual. 



Feb. 9, winds, tides very irregular. Feb. 10 and 11, the same. The 12th, 

 the night tide flowed about 2 feet 10 inches higher than the morning tide. The 

 13th, the night tide flowed about 3 feet higher than the morning tide. The 14th, 

 15th, 16th, 17th, the tides more regular. The 18th, the flood came in much 

 sooner than usual, and seemed to flow gradually at first, but between 1 and 2 

 p. m. the tide flowed several feet, as on a sudden, and continued flowing till \ 

 past 3, being some time longer than it was expected it would, and they had a 

 high tide. The 19th, this day's flood did not hold so long by a quarter of an 

 hour as yesterday's, and not so much water by several feet. The wind being to 

 the westward, and a frost, greatly checked the tide. Since which, the tides 

 have been very regular. 



In a 4th letter from Deptford-yard, similar irregularities were observed. 



LXXIV. And the same in the River, near London, by a Letter from Robert 

 Dingley, Esq. F, R. S., dated London, March 8, 1756. p. 530. 



LXXV. Thoughts on the Rev. Dr. Hales's New Method of Distillation, by the 

 United Force of Air and Fire. By William Brownrigg, M. D., F. R. S. 

 Dated Whitehaven, Dec. 3, 1755. p. 534. 



In the process of distilling sea water, as described by Dr. Hales, the great in- 

 crease of vapour raised by his method, above what is raised by the common 

 method of distillation, may be attributed chiefly to the violent agitation of the 

 water contained in the body of the still, by the motion of the air continually 

 pressed through it. Though the air, by attracting the watry particles, may also 

 contribute to produce this effect. It is however certain, that a simple mecha- 

 nical agitation of warm water will greatly promote its evaporation, by increasing 

 its surface, from which the vapours arise, and by putting its heated particles in 

 a brisker motion, thus exciting between them actions and reactions, and so dis- 

 posing them to fly off in elastic vapours. Of this we have instances in warm 

 water, when simply stirred about in vessels, or poured out of one vessel into 

 another ; from which the vapours visibly arise in larger quantities, than from 

 the same water when it is not moved by such mechanical agitation. 



This excellent invention of Dr. Hales may probably be applied to other pur- 

 poses, besides that which he had principally in view, viz. the distilling of sea- 

 water with greater ease and expedition, with less fuel, and in smaller vessels, 

 than has hitherto been practised, for the benefit of navigators. It might be of 



