. Animal flight; a record of observation . turned into one largedust-devil, which in a moment dissipated. Small dust-devils more usually dissipate suddenlyon contact with some solid object, such as a tree. Thesuddenness of their dissipation and their high speeds ofrotation are facts not easily harmonising with the ideathat they are caused by inrushing currents of air. It is obvious that the larger dust-devils occur soinfrequently, and are so local in their effects, that itis impossible to invoke them as an explanation ofsoarability. CHAPTER XVI. Wind the preceding chapter I have
. Animal flight; a record of observation . turned into one largedust-devil, which in a moment dissipated. Small dust-devils more usually dissipate suddenlyon contact with some solid object, such as a tree. Thesuddenness of their dissipation and their high speeds ofrotation are facts not easily harmonising with the ideathat they are caused by inrushing currents of air. It is obvious that the larger dust-devils occur soinfrequently, and are so local in their effects, that itis impossible to invoke them as an explanation ofsoarability. CHAPTER XVI. Wind the preceding chapter I have shown that, as arule, the kind of soarability that I have described as sun soarability develops at a definite time of theday, and that this time coincides with the appearanceof heat eddies on a particular bastion in the Agra exceptions to this rule hitherto mentioned havebeen cases in which bastion heat eddies do not develop DAYS OF THE MONTH IHf Mff ffi1 ? ¥ 1i4 T 1f V1P y 2r *i1 ^22i3 ¥ y 2i6 7 y7? y 845QSQ£ 8,5807-457-30. J ! 1 1 I I L I I I I I I I I I I I I I I I I I J I I i 1 I Fig. 85. Curves showing daily times of appearance of heat eddies on theBastion by Umar Singh Gate of Agra Fort (continuous line) andtimes of development of sun soarability in Agra city (dotted lines).Both curves refer to the month of April, 1910. owing to part of the energy of the suns rays being cutoff either by the presence of thin cloud or owing to thepresence of masses of dust floating in the air at highlevels. I have now to describe other exceptions whichwill be found to be of an entirely different nature. In fig. 85 the results of certain observations madeduring April, 1911, are shown in the form of continuous line represents the times of appearanceof sun soarability, and the dotted line shows thetimes of appearance of bastion eddies on the different ANIMAL FLIGHT. 279 dates indicated. As shown by the closely superposedcurves there was a connection between developmento
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