144 MICROSCOPIC ILLUSTRATIONS. 



portion of coal into it, which occasions the currents pro- 

 duced by the evaporation to be distinctly seen. The 

 specific gravity of coal not being great, these minute 

 portions are held in suspension during the whole expe- 

 riment. The following observations on this subject are 

 given in the Society's Transactions, vol. 50 : 



1. A drop of spirit of wine, or of naphtha, exhibits two, 

 three, or four vortices, or centres of circulation, accord- 

 ing to the size of the drop ; and if these vortices are 

 viewed laterally, the lines of particles will be seen 

 forming oblique curves from top to bottom of the drop. 



2. Oil of turpentine shews a rapid circulation in two 

 continuous spirals, one to the right, the other to the 

 left, around the drop. These meet in the opposite 

 diameter, from which the particles are slowly carried 

 across the diameter to the place of starting, and this 

 continues while there is fluid enough to let it be seen. 



3. If, however, the drop does not exceed one-tenth of 

 an inch in diameter, it presents the appearance of par- 

 ticles continually rising up in the middle, and radiating 

 in gentle curves to the circumference. 



4. If the liquid be put into a very small phial, similar 

 motions are perceived, the particles, when they have 

 reached the side of the phial, going down to rise up after- 

 wards in the centre or axis. 



5. If a bubble of air be inclosed in the liquid, motions, 

 similar to those described in No. 2, are observed in the 

 part immediately in contact with the bubble. 



