Chemistry and Physics. 505 



destroyed or greatly retarded. In fact, a ring would break 

 through a sheet of tissue paper, but it would be scattered by the 

 impact. Also, a light watch-chain would be bent into a decided 

 curve by a square blow of a ring, hence the kinetic energy of the 

 rings was quite appreciable. When two rings were sent simul- 

 taneously from opposite ends of the tank they would be destroyed 

 if their lines of propagation coincided exactly, but they would 

 separate and avoid one another if they were so aimed as to bring 

 their edges into contact if the rectilinear motion persisted. Inter- 

 nal reflection at the free surface of the acidulated water took place 

 in a beautiful manner when the angle of incidence exceeded about 

 68°. As the surface of the water was approached the upper edge of 

 the ring would gain in speed as compared with the lower edge 

 and the plane of the vortex would tilt in such a manner as to 

 maintain itself always normal to the direction of propagation. 

 For smaller angles of incidence than the critical angle the ring 

 would burst through the surface with a spurt of water. Refrac- 

 tion was also shown by filling the lower half of the tank with a 

 concentrated salt solution, and the upper half with pure water. 

 Vortex rings issuing from a truly circular hole do not vibrate, 

 but rings projected from an elliptical opening exhibit a vibratory 

 motion in their own plane. These vibrations are very rapid and 

 consist in changing from ellipses with vertical major axes to 

 ellipses with the longer axis horizontal. 



Most interesting results were obtained with two circular holes 

 in the muzzle disc of the gun. " The two rings, which issue simul- 

 taneously from the two holes, begin to attract each other the 

 moment they leave the gun, and at a distance from the gun of 

 about 6 to 8 cm they come together with great suddenness, uniting 

 to form a single ring of approximately twice the circumference 

 of one of them." The rings thus formed proceed with the same 

 speed as a single ring, but the vibratory motions are rather com- 

 plicated. The component vibrations can only be fully appreciated 

 by reference to the reproductions of the stereoscopic photographs 

 in which the original paper abounds. 



Experiments were performed which showed that, in the case 

 of two non-miscible liquids of different densities, it is possible to 

 project a vortex of the less dense liquid through the medium of 

 greater density, but it is not possible to reverse the process. For 

 example, a ring of kerosene oil can be projected through water, 

 but a vortex of carbon tetrachloride cannot. By projecting rings 

 of liquid paraffin through hot water and thence into a substratum 

 of cold water, very pretty solid rings of paraffin were obtained 

 and preserved. 



The difficulties attendant upon photographing the vibrating 

 rings were comparatively great and the requisite assemblage of 

 apparatus was too complicated to admit of description in this 

 place. Suffice it to say that full details of the experimental pro- 

 cesses together with a relatively large number of photographic 

 reproductions are given in the September and October numbers 

 (1911) of the Journal of the Franklin Institute. — JVature, Feb- 

 ruary 1, 1912, p. 463. h. s. it. 



