HOLES IN THE AIR 51 



velocity of sound in air at the same temperature, and therefore, at 

 ordinary temperature, of about 1,100 feet per second, or 750 miles per 

 hour. Even then, if such a hole existed, it would be impossible for an 

 aeronaut to get into it — he couldn't catch up with it. 



But, according to the claims of some, if there are no complete holes 

 in the atmosphere there are, at any rate, places where the density is 

 much less than that of the surrounding air; so much less indeed that 

 when an aeroplane runs into one of them it drops quite as though it 

 was in a place devoid of all air and without support of any kind. 



This too, like the actual hole, is a pure fiction that has no support 

 in barometrical records. Indeed, such a condition, as every scientific 

 man knows, could be established and maintained only by a gyration or 

 whirl of the atmosphere, such that the " centrifugal force " would be 

 sufficient to equal the difference in pressure, at the same level, between 

 the regions of high and low density. 



Appropriate equations can be written to express the balance between 

 pressure gradient and centrifugal force in any sort of winds, and at any 

 part of the world (it depends slightly upon latitude). Therefore it is 

 possible with certain conditions given to compute the wind velocity, or 

 with other conditions given to compute the pressure gradient. But in 

 the present case numerical calculations are not necessary. We know 

 that an elevation of half a mile, easily reached by any aeroplane, pro- 

 duces roughly a 1 per cent, decrease in pressure ; and we know too that 

 a greater pressure difference than this seldom exists even between center 

 and circumference of violent tornadoes. Hence a drop in density, or 

 pressure, to which the density is directly proportional, sufficient to cause 

 an aeroplane to fall, would require a tornadic whirl of the most destruc- 

 tive violence. Xow there were no whirlwinds of importance in the air, 

 certainly none that could be called tornadoes, at the times and places 

 where aeronauts have reported holes, and therefore even half holes, in the 

 sense of places sufficiently vacuous to cause a fall, must also be discarded 

 as unreal, if not impossible. 



Along with these two impossibles, the hole and the half hole, the 

 vacuum and the half vacuum, should be consigned to oblivion that other 

 picturesque fiction, — the " pocket of noxious gas." Probably no other 

 gases, certainly very few, have, at ordinary temperatures and pressures, 

 the same density as atmospheric air. Therefore a pocket of foreign gas 

 in the atmosphere would almost certainly either bob up like a balloon, 

 or sink like a stone in water : it could not float in mid air. It is possible, 

 of course, as will be discussed a little later, to run into columns of 

 rising air that may contain objectionable gases and odors, but these 

 columns are quite different from anything likely to be suggested by the 

 expression, " pockets of gas." 



The above are some of the things that fortunately, alike for those 



