140 H. C. RUSSELL. 



thereby add energy to the water-spout, and this intensification 

 would go on until pressures above and below were in equilibrium, 

 or the water-spout became interrupted. Thus Kaemtz's fortunate 

 experience tells us the whole story of the origin and formation of 

 a water-spout. 



In every case the water-spouts on this coast, which have been 

 reported to me, have come from great masses of cloud. (See details 

 in Appendix). As to the extent of these enormous clouds, no 

 special observations have been taken, but the observer at South 

 Head records that one of them, four miles from the coast, extended 

 from south-east to north-east, and therefore must have been at 

 least eight miles long and of considerable breadth, otherwise there 

 would not have been water-spouts under it. The cloud shown in 

 the photograph here reproduced {Plate 7) was distant fully five 

 miles and exceeded considerably the field of view in the camera, 

 which was 80° ; at the lowest estimate the cloud must have been 

 ten miles long and fully half-a-mile in thickness or vertical depth. 

 The cloud mass at Eden was large and conspicuous when it was 

 thirty miles away. 



It is obvious that such masses of cloud, resting over warm water 

 in calm or almost calm weather, must be in a state of unstable 

 equilibrium. The want of wind allows the warm humid air to 

 accumulate under the great extent of cloud, being warmer than 

 the surrounding air its tendency is to rise. The cloud itself is in 

 unstable equilibrium, the parts constantly readjusting themselves 

 with much energy, as can be seen with aid of a telescope. This 

 motion at times causes partial breaks, as seen at A Plate 7 from a 

 photograph of such a cloud, when this break makes the cloud weak 

 enough for the confined, heated, and moist air below to force its 

 way through, this confined air rushes up through the cloud taking 

 on a vortex motion, and its moisture condenses as it rises, increas- 

 ing the partial vacuum and accelerating thereby the uprush. The 

 energy of the water-spout depends then upon the temperature and 

 moisture of the air below, and the vertical thickness of the cloud, 

 through a hole or pipe in which the heated air finds a vent into a 



