38 l.VDEPENDENT OF THE LAW OF GRAVITY. 



expanded or contracted. Yet would it seem that in this 

 plausible doctrine of vacuity there may be a congenial nothing 

 after all ; its supposed facts of foundation seeming to vanish 

 before the asserted power of our little pedestrian to traverse 

 the sides and stick fast to the dome of an exhausted receiver. 

 If then it be not by a vacuum, by what something is it that 

 she does retain her hold? Mr. Blackwall, who tried the 

 experiment of the receiver, found also that a Fly, enfeebled by 

 cold or other causes, would climb with difficulty the sides of a 

 glass, ascended before with perfect ease. Further, he observed 

 that Flies unable to stand, back downwards, on highly polished 

 bodies, were able to do so on those slightly soiled ; and from 

 these and other observations, considers that the apparatus 

 whereby they effect their hold is quite mechanical, and closely 

 analogous to the pulvilli or fine hair brushes of other Insects 

 used as holders or supporters. This modern notion nearly 

 agrees with that set forth almost 200 years ago by a Dr. Power,* 

 who says that " the Fly is provided with six legs, and walks 

 on four. The two foremost she uses as hands wherewith to 

 wipe her mouth and nose, and take up what she eats, her 

 other four feet are cloven and armed with little claws, by which 

 she fastens on rugosities and asperities of all bodies, like a 

 Cat-a-mount. She is also furnished with a kind of fuzzy 

 substance like little sponges ''' (these are our suckers) " with 

 which nature hath lined the soles of her feet, which substance 



* Dr. Power's Experimental Philosophy, 1664. 



