130 Mayow 



from the centre of the vortex to its outer edge, but 

 where the air is rarer the aqueous particles can more 

 easily continue their movements ; and, turned back 

 in this way, they arrive at last at the middle of the 

 aerial vortex (which behaves like a vacuous tube), and, 

 congregated densely there, are carried aloft in a 

 swift whirl and spiral revolution, as is shown in the 

 figure. Moreover the spiral motion of those vapours 

 arises from the circular motion of the surrounding air. 

 To bring the said vapours to the middle of the aerial 

 vortex, and thence to raise them on high, the pressure 

 of the atmosphere seems to contribute not a little, in 

 addition to the force by which they have been torn 

 from the mass of water. For since the air at the 

 summit of the atmosphere is much rarer than that 

 which is nearer the earth, and its pressure less, and 

 since, also, the aerial vortex rotates there more rapidly 

 (for the force which constrains the air to rotate prob- 

 ably comes from above), it follows that the force by 

 which the aerial particles strive to recede from the 

 centre of their motion will take effect much more 

 easily at the summit of the atmosphere than near the 

 underlying water ; so that high up in the air where, 

 namely, the said tube is seen, the aerial particles 

 recede from the centre of the vortex and are able to 

 produce a vacuum there, whereas the air from the 

 lower end of the tube to the underlying water, being 

 rotated less rapidly, is merely able to diminish the 

 pressure of the atmosphere, which is greater there, 

 but not altogether to remove it ; and hence, the air 

 and vapours at ^, e (where the vacuous tube begins), 

 are driven forcibly into the tube by the pressure of 

 the surrounding air. Further, as all the neighbour- 

 ing particles of air and vapours come into the place 

 of those that have been carried up, and others again 



