in Fluids. 389 



3^ Experiment . — When this experiment was varied by 

 using a flat cake of tallow instead of a cake of ice, a 

 very extraordinary appearance indeed presented itself, 

 which at first surprised me very much, but which I soon 

 perceived was a new and very striking proof that Fluids 

 are non-conductors of Heat. 



The bottom of the circular cavity in the cake of tal- 

 low which was occupied by that part of the tallow that 

 had been melted in the experiment, instead of being con- 

 cave, as I had found that in the ice to be, or flat, as 

 I expected to find this, was convex in the middle, or 

 rather rose up in the form of a protuberance, or very 

 blunt point, the extremity of which reached almost to 

 the surface of the melted tallow! As the iron bullet 

 was held as near as possible to the tallow, the end of this 

 projection, which remained unmelted, was certainly not 

 more than -^-^ of an inch distant from this red-hot ball ! 

 Reflecting on the unexpected result of this experiment 

 I was much struck, and not a little humiliated, with the 

 proof it seemed to me to afford of the impossibility of 

 predicting with certainty any event, however inevitable it 

 may appear, which has not actually been seen to happen. 



Though I well knew how the Heat must be commu- 

 nicated under the given circumstances, and could foretel 

 with certainty the directions of the currents it must ne- 

 cessarily occasion in the melting tallow ; yet the utmost 

 eflxirts of my intellectual powers, exercised as they were 

 by much meditation, were not sufficient to enable me to 

 foresee that the point where least Heat would be commu- 

 nicated was that precisely which was nearest to the red- 

 hot bullet, and that a protuberance of unmelted tallow 

 would be left in that place. 



Let those be very cautious who speculate on the sup- 

 posed results of experiments they have never made ! 



