FREDERICK GUTHRIE ON THE THERMAL RESISTANCE OF LIQUIDS. 657 
the conclusions drawn by Herr Magnus from his experiments have been questioned by 
Dr. Tyndall and other physicists, I refrain from doing more than point out this distinct 
coincidence. 
§ 65. Of bodies belonging to the same chemical series or isotypic bodies, those have 
the least thermal resistance which have the simplest constitution. Thus the resistances 
of the three alcohols examined are in the order amylic, butylic, and ethylic. Again, 
the acetate of amyl has greater thermal resistance than the acetate of ethyl, and the 
oxalate of amyl than the oxalate of ethyl. The only exception to this appears to be the 
iodide of ethyl in comparison with the iodide of amyl ; but, as before stated, I am dis- 
posed to reject the determination of the former body. 
§ 66. The only one of these liquids which contains a metal is mercury amyl, and this 
was tried under the expectation that, owing to the chemical construction of the body, 
the metallicity of the mercury in regard to its conductivity might appear. Contrary to 
anticipation, the liquid has one of the greatest resistances. 
§ 67. Another noteworthy circumstance is the great specific resistance of all the 
liquids which contain halogens. May it be owing to the halogenous function of the 
mercury in the mercury amyl, which brings that liquid to so low a place 1 
The existence of these regularities and consistencies supports, at all events, the 
approximate and relative accuracy of the determinations, and by furnishing a new 
equation of physical property, opens a wide field for future research. 
§ 68. If the results just given concerning thermal resistance be compared with those 
of Signor Melloni and Dr. Tyndall with regard to diathermancy, and especially with 
those of the latter philosopher concerning the absorption of radiant heat by various 
liquids, a striking dissimilarity at once appears. Taking the four liquids common to 
both, water, alcohol, acetate of ethyl, and chloroform, Dr. Tyndall found that of 100 
heat-rays of an Argand burner they absorbed — 
Water (saturated with Na Cl) 86T 
Alcohol 78'6 
Acetate of ethyl 74'0 
Chloroform 25’0 
respectively when the thickness was (M)4 inch (1 millim.==0 , 03937 inch). These liquids 
are accordingly in exactly the inverse order to that in which they appear in the Table, 
§ 60*. That this apparent contradiction is in fact a coincidence appears from the fol- 
lowing considerations. 
§ 69. The diathermancy of a liquid towards radiant heat, and its resistance to contact 
heat, are partly due to one and the same cause. The amount of absorption of radiant 
heat by a liquid, as determined by Dr. Tyndall, is estimated by the quantity of heat 
which passes through the body so as to affect the thermomultiplier; and the amount 
of absorption is directly proportional to the athermancy. Now a liquid which absorbs 
* To my great regret I have not yet been able to determine the resistance of bisulphide of carbon; but I 
scarcely hesitate to predict that it has a very great, perhaps the greatest thermal resistance. 
