between Metallic Masses having different Temperatures. 23 



20. In pursuing these experiments, I varied them in every 

 way I could devise, but almost always got precisely the same 

 arrangement of vibrators. Employing a lead bar, I used also 

 blocks of the different metals heated to 212°. With silver, 

 gold and platinum, I found it difficult to procure considerable 

 masses of sufficient purity; and when small ones taken out of 

 boiling water were employed and placed in a vice, I found 

 that the loss of heat they experienced was so rapid as to de- 

 stroy the comparability of the experiment. The plan I adopt- 

 ed for procuring an approximation to a uniform tempera- 

 ture, and which from reiterated trials I found susceptible of 

 great accuracy, was the following : The piece of metal under 

 experiment being firmly held in a vice, a drop of water was 

 placed upon it, and a spirit-lamp applied below, so as to heat 

 at once the metal and the vice, until the water was I'apidly 

 dissipated in the act of ebullition, at which instant the cold 

 bar of lead was placed upon it, and the vibrations encouraged 

 by a gentle oscillation. In this manner I went over not only 

 the metals which could not be conveniently tried in the other 

 way, but also those of which I already had bars. 

 . 21. Pursuing the relations of the metals to cold lead, I 

 found, in the first place, that the position of platinum is not 

 very different from that of tin. The mass used weighed about 

 7 ounces, and was kindly lent to me by Dr. Hope ; its form 

 prevented its being used as a bar, and its small thickness and 

 angular corners did not fit it for retaining a high temperature, 

 or performing well the part of a block. When held in a vice 

 and heated by a spirit-lamp, the vibrations of a cold lead bar 

 were very active. From some experiments made with iron, 

 tin and platinum, at a temperature of 350°, I conceived that 

 they stood as vibrators in the order just named : I had not 

 then, however, fallen upon a method of operating upon small 

 masses with accuracy ; and subsequent experiments, often re- 

 peated, with a small thick mass lent me by Professor Jameson, 

 and heated till water boiled on the surface (as above ex- 

 plained) led me to tha conclusion, that, in the other mode of 

 experimenting, platinum had been placed too low, as might 

 have been anticipated, and that it is at least equal to iron in 

 vibrating power. It appears at the same time that there is 

 little difference between platinum, iron and tin. 



22. From numerous experiments with antimony and bismuth, 

 these metals when heated appeared to have no vibratory ac- 

 tion with cold lead. This experiment was tried at a great 

 range of temperatures, and, notwithstanding the low melting 

 point of bismuth, I raised it by a particular arrangement to a 

 temperature of 350 J without obtaining any vibration. 



