140 . Experimental Investigations 



stance, but by the action of colder surrounding bodies, 

 communicated by undulations or radiations excited in 

 an ethereal fluid, the results of this experiment may 

 be easily explained ; but, if this hypothesis be not 

 adopted, I cannot explain them. 



It might, perhaps, be suspected that the air attached 

 by a certain attraction, but with unequal forces, to the 

 surfaces of the two bottles, might have been the cause 

 of this remarkable difference in the time of their cool- 

 ing ; but those who will take the trouble to reflect 

 attentively on the results of the experiments I have 

 described in a preceding Memoir, which were made with 

 a view to clear up this point, with a metallic vessel first 

 naked, and afterwards with one, two, four, and five coat- 

 ings of varnish, will be persuaded that this cause is not 

 sufficient to explain the facts. 



By a course of experiments made at Munich, last 

 year, of which the details are given in a Memoir sent to 

 the Royal Society of London,* I have found that a 

 given quantity of hot water, included in a metallic ves- 

 sel of a given form and capacity, always cools with the 

 same quickness in the air, whatever may be the metal 

 employed to construct the vessel ; provided always that 

 the external surface of the vessel be very clean, and the 

 temperature of the air the same. 



In order that the cooling shall be effected in the same 

 time, nothing more is required than that the external 

 surface of the vessel be truly metallic, and not covered 

 with oxide, or other foreign bodies. 



On the inquiry, what quality all the metals might 

 have in common, and possess in the same degree, to 

 which this remarkable equality of their susceptibil- 



* See p. 23. 



