in Fluids. 271 



Though the greater number of these particles seemed 

 at first to have no tendency either to ascend or to descend, 

 yet some of them soon began to move very slowly up- 

 wards, and others to move as slowly downwards ; and as 

 these particles were moving at the same time promiscu- 

 ously in all parts of the same liquid, and even in the 

 same part of it in both directions at the same time, the 

 ascending and descending particles frequently passing 

 each other so near as to touch, I saw that these motions 

 were independent of any internal motion of the liquid, 

 and arose merely from the difference of the specific 

 gravity of the different small pieces of the amber and 

 of that of the liquid. Some of the pieces of amber, 

 being evidently heavier than the liquid, moved down- 

 ward, while others which were lighter ascended to its 

 surface. 



Finding that there was so much difference in the spe- 

 cific gravities of the different pieces of amber, I now 

 added more of this substance to the liquid, and suffering 

 it to subside after I had shaken it well together, I gently 

 poured off what had risen to the top of the liquid, and 

 retaining only that which had settled at the bottom of it, 

 I increased the specific gravity of the liquid by adding a 

 little of the alkaline solution till the small pieces of am- 

 ber which remained in the glass were just buoyed up and 

 suspended in the different parts of the Fluid, where they 

 seemed to have taken their permanent stations. 



I had now an instrument which appeared to me to be 

 well calculated for the very interesting experiments I had 

 projected, and it will easily be imagined that I lost no 

 time in making use of it. 



The first experiment I made with this instrument was 

 to plunge it into a tall glass jar nearly filled with water 



