220 MEANS BY WHICH ANIMALS ADHERE 
pose or an increase of temperature, they again repeated 
their most extraordinary feats with all their original 
promptness and dexterity. 
Flies which are unable to maintain an inverted 
position on highly polished bodies will frequently 
adhere firmly, with their backs downward, to glass 
rather defective in polish or slightly soiled; indeed 
I may remark generally -that the results of expe- 
riments similar to those detailed above will always 
be modified by the vigour of the insects and the 
state of the glass vessels with regard to cleanness and 
polish. 
These facts plainly indicate that flies are not sup- 
ported on: the vertical sides of smooth bodies by the 
pressure of the atmosphere; and the only link in the 
chain of evidence which was wanting to place the 
matter beyond all dispute, the kindness of Mr. W. 
Hadfield, of Cornbrook, has enabled me to supply. 
With his assistance and the help of his air-pump it 
was proved, to the entire satisfaction of several intel- 
ligent gentlemen present, that the House-fly, while it 
retains its vital powers unimpaired, can not only tra- 
verse the upright sides, but even the interior of the 
dome of the exhausted receiver; and that the cause 
of its relaxing its hold, and ultimately falling from 
the station it occupies, is a diminution of physical 
energy attributable to impeded respiration. To this 
circumstance in particular, as furnishing an experi- 
mentum crucis by which the fallacy of the prevailing 
