332 A. Wing's Discoveries in Vermont Geology. 



the aid of the mouth, one can fill this tube with liquid and 

 eject it in drops at pleasure. The same apparatu 

 to form the rings beneath the surface of the liquid. With a 

 tube bent horizontally, one can send the rings through a liquid 

 in any desired direction: and, by means of a three-way glass 

 joint and a small india-rubber bag, one can send forth, bj the 

 same impulse, two rings whose paths make any desir 

 with each other. By partly immersing the glass tubes connected , 

 with the three-way tube in the free surface of the liquid, and 

 covering the surface of the water with fine powder, one can study 

 the mutual behavior of half vortex rings. A simpler method is 

 to illuminate, by means of a gas-light, the bottom of a flat, white 

 porcelain dish filled with water, and to observe the shadows of 

 the half-vortex rings on the bottom of the dish formed by the 

 movement of two spatulae along the surface. It can be readily 

 seen, by this simple method, that a half-vortex ring moving 

 near another in a parallel path and with a less velocity tends to 

 follow in the path of the first ; and that two equal half-vortex 

 ring in opposite directions along the same path separate 

 vortices which move at right angles to the path of the 

 original vortices. We can conclude, also, from this general dis- 

 cussion, that, whenever a mass of vapor of greater density than 

 the surrounding air is suddenly formed in the higher regions of 

 the atmosphere, it tends to descend through it in a vortex ring. 

 The results of the preceding discussion are as follows : 



1. An analogy between the strain potential and the velocity 

 potential is indicated. 



2. It is shown that the formation of liquid rings is a necessary 

 result of the fundamental equations of strains and those of 

 hydrodynamics ; and that they constitute a general and not a 

 special phenomenon. A drop of water falling into water from 

 a suitable height must assume a ring shape. 



3. Vortices can and do arise in certain processes of diffusion. 



4. Simple methods of studying vortex motion in liquids are 

 given. 



Art. XXXVni.— An account of the Discoveries in Vermont Geol- 

 ogy of the Rev. Augustus Wing ; by James D. Dana. 



The death of the Rev. Augustus Wing, in January, 1876, 

 deprived the country of an excellent geological observer, and 

 science of the results, to a large extent, of his long labors* 

 JJunng the preceding summer, in July, I had the pleasure of an 

 excursion with him to various localities over the country between 



