GOSSAMER 245 



reason that impalpable drops of water form mists and 

 clouds, instead of sinking at once to the earth. The 

 smaller the particles, the greater the ratio of surface to 

 volume, the greater the ease of transport by a current, 

 and the greater the resistance to falling through air or 

 water. If we divide a sphere into spheres of -J, J, J, 

 etc., the original diameter, the aggregate surfaces 

 increase as 2, 3, 4, etc. The same is true of a cylinder 

 or any other figure, provided that the parts are similar 

 in shape to the original figure. It is a general and 

 well-known law that the surfaces of similar figures 

 increase as the square, but the volumes or weights as 

 the cube of any linear dimension. Hence, if the scale 

 is enlarged, the weight gains upon the surface ; if 

 reduced, the surface gains upon the weight. Take a 

 knitting needle T V inch in diameter. Reduce it in all 

 its dimensions until the diameter becomes T0 -J(nr inch, 

 which is of the order of fineness of a thread of 

 gossamer. The surface is reduced to (roWo) 2 , the 

 weight to GoVW) 3 ! tnat is > tne surface gains on the 

 weight about 625 times. The actual knitting-needle 

 falls quickly through the air, while the reduced 

 knitting-needle, if we could make such a thing, would 

 fall slowly, for the resistance of the air in proportion to 

 the weight has been increased 625 times. Not only 

 do the lightest breezes set up by differences of atmos- 

 pheric pressure suffice to waft the Spiders, but they 

 ascend when there seems to be no movement in the 

 air, except the ascending current due to the heated 

 ground. Such currents will cause soap-bubbles to 

 ascend, which will not rise in-doors. 



Incomplete information prevents us from clearing 



