350 Prof. Buff on the Escpmment of Leidenfrost. 



of waxy or resinous matter* evidences that it could not be pure 

 wine, but either one of the compounds alluded to, or mulsum ; 

 most probably the former. As the Eomans derived many of 

 their customs from the Greeks, so in turn the Greeks in all 

 probability borrowed from the Egyptians, with whom they held 

 frequent intercourse. It has been suggested to me, that the 

 matter contained in the bottle was a kind of varnish employed 

 to fix the fresco-paintings adorning the Egyptian tombs, which 

 might be a solution of some waxy or resinous substance in wine ; 

 but I am disinclined to this opinion, on account of the large 

 quantity of red colounng matter extracted by water, as well as 

 the small portion of residue contained in the bottle. 



The I'ed colouring matter was very analogous in its characters 

 to that in port wine, but it had evidently undergone gradual and 

 partial change into humic acid and insoluble humus. These 

 together constitute above one-third of the whole organic matter. 

 The large quantity of ashes is partly owing to the admixture of 

 loose sand from the sides of tlie bottle, and to what must have 

 penetrated from without in so sandy a country as Egypt. 



XLVII. On the Experiment of Leidenfrost. Extracted from a 

 Letter from Professor Buff to Professor Tyndall. 



My dear Sir, 



WHEN I consider how well grounded your views are with 

 regard to the origin of the phgenomenon described by 

 Trevelyn, I am surprised to find, with reference to another of the 

 phsenomena of heat, namely the experiment of Leidenfrost, that 

 the theory of a repulsive action at a distance by heat seems to find 

 favour in your eyes. At least I must conclude so much from a 

 casual remark in a memoir upon the subject by Mr. A. Church. 

 Mr. Church mentions an experiment, which he witnessed in your 

 lectures, by which you show that water in the spheroidal con- 

 dition interrupts the passage of an electric current to the red-hot 

 metal underneath*, and observes that you regard this experiment 

 as a proof that the surface of the vessel is separated by an in- 

 terval from the drop within it. 



The same experiment has been often made and observed under 

 various conditions by myself, but I am not able to ascribe to it 

 the same force of proof. I only find that the passage of elec- 

 tricity through water in the spheroidal state is rendered ex- 

 tremely difficult, and solely because the points of mutual con- 

 tact between water and metal are reduced to a comparatively 



* M. PoggendorfF was, I believe, the first to perform this experiment. 

 — J. T. 



