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XXII. On the Thermal Resistance of Liquids. By Frederick Guthrie. 
Communicated by Professor Tyndall, LL.L., F.JR.S. 
Beceived October 16, 1868, — Bead January 21, 1869. 
I. Introduction. 
§ 1. The passage of heat through matter has been mainly examined in reference to the 
diathermancy of solids, liquids, and gases to radiant heat, and to the conduction of con- 
tact-heat through solids and gases. The conduction of contact-heat through liquids 
forms a chapter in heat transference which has not hitherto received as much attention 
from experimental physicists as it merits. 
§ 2. In the following pages I have the honor of submitting to the Royal Society 
certain experimental results and considerations to which I have been led during an 
investigation of this subject. These results are necessarily incomplete. The inquiry is 
fraught with very numerous and considerable experimental difficulties ; but I venture 
to hope that such as the results are, they may be found useful to those who shall here- 
after pursue the subject with greater skill and more perfect appliances. 
§ 3. It need scarcely be stated that the great majority of the experimental results 
obtained do not appear in this Memoir. Such results, though of great interest to the 
experimenter and invaluable for his guidance, have of course been suppressed, having- 
been superseded during the investigation by those obtained through the application of 
successive improvements to the apparatus employed. 
§ 4. I have been induced to pursue this investigation with some perseverance, because 
I am convinced that it is by means of liquids rather than of solids that we are destined 
to gain ultimately an exact experimental determination of the conduction of heat in all 
cases. By their means we shall gather data concerning the conductive indices or thermal 
resistances of the elements, and be able to determine the effect on such resistance caused 
by the change of chemical nature and of molecular construction of bodies. 
§ 5. These data will be furnished by liquids rather than by solids, because no two 
specimens of the same solid substance are physically identical. It would be difficult, 
perhaps impossible, to point to a single solid the material of which has not, at some 
time or other, been in the liquid or gaseous state. Now, in the overwhelming majority 
of instances, the parts of the body, at the moment of solidification, arrange themselves 
in some definite form, either as the rectilinear crystals of definite chemical proportion, 
or as those more complex forms wrought together by living beings. And it is owing 
to the varying conditions under which such solidification takes place, that the structure 
of different specimens of solid matter bearing the same name is so various. 
MDCCCLXIX. 4 Q 
