New Brunsioick Tornado. 75 



11. The sudden and extraordinary diminution of the atmos- 

 pheric pressure which is said to take place at the points succes- 

 sively passed over by a tornado, causing the doors and windows 

 of buildings to burst outwards, seems to afford strong confirma- 

 tion of a violent whiding motion ; for an effect of this kind is 

 necessarily due to the centrifugal and upward force of the vortic- 

 ular action in the interior portion of the whirlwind. There are 

 no other means known by which such an abstraction of pressure 

 can be effected in the open air. An increase of calorific elasti- 

 city, if such were produced, either generally or locally, would not 

 greatly disturb the equilibrium of pressure, being resisted by the 

 surrounding and incumbent weight of the entire atmosphere. 

 Besides, the immediate effect of such increased elasticity might 

 rather be to burst inward the windows and doors of buildings 

 exposed to its action. 



Some of the more important indications mentioned above ap- 

 pear also from an examination of Prof. Bache's observations ; 

 although the latter are not definitely located by him, as regards 

 the extreme borders of the track. Thus, in Fig. 7 of Professor 

 Bache's paper, assuming the course of the tornado to be east, 

 and rejecting a few observations near the centre, to avoid error, 

 we find in twenty observations on the right side of the track, a 

 mean inward inclination of 64 degrees ; and for nine observa- 

 tions on the left side, a mean inclination, reckoned inward and 

 backward from the course, of 104 degrees, being 14 degrees 

 backward. 



It is stated by Prof. Bache, " that the trees lying perpendicu- 

 lar to the track of the storm, are not those furthest from the cen- 

 tre of that track." This generahzation accords with my own 

 observations ; but can hardly be reconciled with an inward non- 

 whirling motion in the tornado. 



It may appear to some, that in the case of a whirlwind the 

 greater portion of the prostrations on the reverse side of the axis 

 should be found in a backward direction ; and so they would 

 undoubtedly be found, were it not for the inward and the pro- 

 gressive action. But the force is here so far lessened by the re- 

 verse action above noticed, that in most cases only a small portion 

 of the trees exposed will be thus prostrated ; while the greatest 

 force of the whirlwind, on this side, is felt near its last or closing 

 portion and towards the apparent axis, where the inward, together 



