472 Miscellaneous I?itelUgence. 



II. Chemical Science. 



1. On the Conducting Power of Bodies for Heat, and on a new 

 instrument called a Thermometer of Contact, by M. Fourier. — A 

 memoir on these subjects by M. Fourier is inserted in the 

 ' Annales de Chimie, xxxvii. p. 291/ which contains not only the 

 description of two new instruments, with their applications and 

 some novel results obtained by their means, but also the mathe- 

 matical developement of the theory of these instruments, and of 

 the experiments made with them. 



The instrument called a thermometer of contact, consists of a 

 conical vessel constructed of very thin iron, with the exception of 

 the bottom, which is made of thin pliable skin ; it is filled with 

 mercury and has a thermometer, the bulb of which is immersed 

 entirely in the mercury, and the scale has degrees of such mag- 

 nitude that they may be divided into tenths. The skin must be 

 preserved perfectly clean and never be overheated : it is better 

 than any other similarly flexible substance, because of its superior 

 conducting power. This instrument is to be accompanied by a 

 support consisting of a block of marble 3 and any substance 

 operated upon is to be in sheets or reduced to thin plates. When 

 an experiment is to be made, the sheet, cloth, or thin plate is to be 

 placed upon the marble, both being at the temperature of the 

 room ; the conical vessel, with its contents, is to be heated on a 

 stove or other hot body, until about 46° or 47° C. j and then being 

 removed, at the moment it has fallen to 45°, it is to be placed on the 

 substance to be tried ; the time when it arrives at 40° is to be 

 exactly noted by a watch, and then the temperature noted minute 

 by minute for five minutes. If the experiment be repeated with 

 the same substance on another part of the marble, exactly the same 

 results will be obtained, provided the temperature of the place 

 has not changed. If the experiments are to be made on rigid 

 plates, tlien these are not to be placed directly upon the marble., 

 but upon a mercurial cushion, made by confining mercury under a 

 surface of skin. 



If the substance first tried be replaced by another, and then 

 the fall of temperature in a given time be noted, the variation 

 will be found very sensible, however slight the difference between 

 the substances 5 the addition of a single sheet of the finest paper 

 makes a great difference in the effect. The slightest difference in 

 the nature of the stuff is immediately indicated. If a piece of 

 linen cloth be replaced by flannel, or by woollen cloth, or a thin 

 piece of woollen cloth by a thick piece, not only are the differ- 

 ences produced very evident, but they can be obtained over and 

 over again with the utmost constancy, care being taken that the 

 pressure of the mercury upon the skin, and therefore upon the 

 substance, be the same in all cases. 



The same instrument also indicates the heat of contact of 

 bodies. In such cases, after being heated as before mentioned, it is 



