646 
FREDERICK GUTHRIE ON THE THERMAL RESISTANCE OF LIQUIDS. 
AH X 
Water alone, 
millims. 
113-41 
Water with paper disk, 
millims. 
108-58 
ah 2 
203-61 
203-61 
ah 3 
243-71 
243-71 
ah 4 
267-84 
262-91 
ah 5 
282-34 
277-39 
ah 6 
291-97 
287-04 
ah 7 
301-62 
296-69 
ah 8 
308-76 
304-04 
ah 9 
313-69 
311-18 
AH 10 
316-10 
316-10 
The absolute coincidence of some of these numbers to the second place of decimals 
arises from the arbitrary divisions on the scale being reduced to millimetres, and is not 
therefore a measure of the strictness of the accord. Nor can these results be compared 
with those of § 34 for the reasons given ; but they bear strong independent testimony 
to the absence of sensible radiation. 
§ 37. As, however, Dr. Tyndall has deduced from his experiments on radiant heat 
that water (or at all events a saturated solution of chloride of sodium) is of all transpa- 
rent liquids examined the most athermanous, it was considered advisable to examine 
one or two other liquids. On examining amylic alcohol and oil of turpentine in this 
manner, the depression in Q, when the liquids were alone, was found to be even more 
strictly equal to that produced in the presence of a paper disk than was shown by water. 
The most recent researches of Herr Magnus * entirely confirm these results. This 
experimenter has shown that a certain proportion of non-luminous heat-rays which 
radiate at an angle of 35° from the surfaces of solids and liquids heated to 100° C. 
undergo polarization, and that consequently a certain proportion of the heat radiated in 
this way emerges from beneath the geometrical surface of the body. It would result 
from this conclusion that all the substances examined are, up to a certain thickness, dia- 
thermanous. Such superficial diathermancy is quite consistent with the perfect ather- 
mancy of the same substances when employed in sheets or films of the utmost attainable 
tenuity. 
§ 38. The same experimenter has, indeed, shown that when a liquidis raised throughout 
to 100° by maintaining its lower portion at that temperature, precisely the same pheno- 
mena of radiation and polarization of the heat are observed, whether the bottom of the 
vessel containing the liquid be brightly polished or covered with lampblack. It results 
from these experiments that the liquids examined, namely rape-oil, resin, wax, glycerine, 
paraffin, in layers less than 1 centimetre f in thickness, are perfectly athermanous to 
* Monatsbericht der Koniglich preussischen Akademie der Wissenschaften zu Berlin, April 1868, p. 249. 
t The liquid was contained in a metallic dish 1 centimetre deep ; tbe exact thickness of the liquid layer is 
not stated. 
