i:3 , '.ling in Vacua. [Book II. 



rcftored *. In the moil perfect vacuum ihat we are 

 able to procure water boils at 90, and fpirit of wine at 

 52, that is at 122 below the boiling point under the 

 common preffure of the atmofphcre. 



A pleafmg experiment is related by that elegant and 

 ingenious philolbpher, the prefent Biihop of Landaf}^ 

 which is fllufrrative of the nature of boiling in general, 

 and particularly of what has been juft advanced. With 

 an intention of exhibiting a linking inftance of the in- 

 creafe of dhnenfions produced by heat in fluids, he 

 took a glafs vefTel, not unlike a thermometer in form; 

 the bulb contained above a gallon, the ftem had a 

 fmall diameter, and was about two feet in length. 

 This veflel he' filled with boiling water to the very top 

 of the ftem, and corked it dole with a common cork. 

 The water and the cork were at firft contiguous, but 

 as the water cooled it contracted, and funk vifibly in 

 the ftem ; and thus the firft intention of the experiment 

 was anfwered.' But here an unexpected phenomenon 

 prefented itfelf. The water, though it was removed 

 from the fire, though it was growing cold, and had for 

 fome time entirely ceafed from boiling, began to boil 

 very violently. When a hot iron was applied to that 

 part of the ftem, through which the water in contract- 

 ing itfelf had defcended, the ebullition prefently ceafed ; 

 it was renewed when the iron was removed j and it 

 became more than ordinarily violent, when by the ap- 

 plication of a cloth dipped in cold water that part was 

 cooled. To account for thefe appearances, it is only 

 cecefiary to recollect, that by the finking of the water 

 in the ftem a kind of vacuum is left between its fur- 

 face and the ccrk; the water therefore necefiarily boils 

 with a lower degree of heat than it would- under the 

 preffure of the atmofphere. The fpace- between the 



* Higgins's "Experiments and Obfervations, p. 313. 



cork 



