in various Substances. 



45; 



The experiment No. 25 was simply a repetition of 

 that numbered 24, and was made immediately after it ; 

 but, in moving the thermometer about in the former ex- 

 periment, the powder of charcoal which filled the globe 

 was shaken a little together, and to this circumstance I 

 attribute the difference in the results of the two experi- 

 ments. 



In the experiments with lampblack and with wood- 

 ashes, the times taken up in cooling from 70° to 60° 

 were greater than those employed in cooling from 60° to 

 50^" ; this most probably arose from the considerable 

 quantity of Heat contained by these substances, which 

 was first to be disposed of, before they could receive 

 and communicate to the surrounding medium that which 

 was contained by the bulb of the thermometer. 



The next experiment I made was with semen lycopodii^ 

 commonly called witch-meal, a substance which possesses 

 very extraordinary properties. It is almost impossible 

 to wet it ; a quantity of it strewed upon the surface of a 

 basin of water, not only swims upon the water without 

 being wet, but it prevents other bodies from being wet 

 which are plunged into the water through it ; so that a 

 piece of money, or other solid body, may be taken from 



