On the non conducting power of Water. 3G9 



jection, Dr. Murray made the experiment in a vessel of ice, 

 which being converted into water at 32° cannot convey any 

 degree of heat above 32° downwards, yet the thermometers 

 were affected as in the former trial." From this experiment, 

 Dr. Murray draws his conclusion, that water is a conductor 

 of heat downwards. Is it not as probable that the thermom- 

 eters beneath the surface of the water (in the preceding ex- 

 periment,) were affected by radiant heat from the heating 

 body, as by conducted heat ? This question suggested itself 

 to me while reading the preceding experiment. It is a well 

 known fact, that highly polished metals, reflect radiant heat 

 perfectly, and are excellent conductors. If then in the ap- 

 paratus used by Dr. Murray, a burnished metallic disk be 

 placed between the surface of the water and the thermom- 

 eters, it is evident that it would not prevent the passage of 

 caloric by conduction, so that should the thermometer be 

 affected under these circumstances, it would show that water 

 did conduct heat downwards. All heat that might radiate 

 from the heating body, in the direction of the thermometers, 

 would be reflected off by the disk, so that all possibility of 

 caloric passing from the heating body, except by conduction, 

 is intercepted. During the months of January and February 

 last, I made many experiments upon this subject. I am un- 

 der many obligations to Dr. Torrey for his assistance, and 

 for furnishing the necessary apparatus. The first few exper- 

 iments were of no avail, from the circumstance that the ther- 

 mometer was not of sufficient delicacy to detect a change of 

 temperature, either when the plate was, or was not interposed. 

 An air thermometer was then constructed, of such delicacy 

 that a change of temperature of T |„ of Fahrenheit, would 

 drive the bead of fluid along the stem one inch. 

 The stem of the thermometer was luted into the tu- 

 bulature of a common gas receiver, so that when the 

 receiver was inverted and filled with water, the bulb 

 was covered to the depth of from half an inch to one 

 inch. The receiver was coated internally and ex- 

 ternally with ice, from half to three quarters of an 

 inch in thickness, placed upon a stand, and filled 

 with water, which (having ice dissolving in it) re- 

 mained at 32°. A few drops of ether were poured 

 carefully upon the surface and inflamed. The bead 

 of fluid moved along the tube about one inch, indi- 

 cating a change of temperature in the air of the 

 Vol. XIII.— No. 2. 22 



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