zvhose progressive motion is against gravity. 15$ 
magnified, such is the liability to error, that any person with a 
preconceived opinion becomes an improper observer of the 
appearances that are represented. From this consideration, 
I have not examined them myself, but have rather chosen to 
refer to the representation of their structure taken by others. 
Mr. George Adams, mathematical and optical instrument 
maker, in Fleet-street, London, in the year 174,6, published a 
plate representing the appearance of the fly’s foot when highly 
magnified. This figure will be found at the end of the paper. 
His account of the uses of the different parts is by no means 
satisfactory, but he concludes it by saying, “ That the fly is 
enabled to walk on glass, proceeds partly from a ruggedness 
of the surface, or a kind of tarnish, or dirty, smoaky substance 
adhering to the surface of that very hard body; and though 
the pointed parts (of the fly’ s foot) cannot penetrate, yet they 
may find pores enough in the tarnish, or at least make them. 
This structure Mr. Hook surveyed with great diligence, be- 
cause he could not comprehend, that if there was any such 
glutinous matter in those supposed sponges (as most that have 
observed that object in a microscope have believed), how the 
fly could so readily unglew and loosen its feet ; and also be- 
cause he had found no other creature any ways like it.” Jean 
Christofle Keller, painter at Nuremberg, made a drawing 
of the fly’s foot in a highly magnified state, which was pub- 
lished in 1766. The author of the publication to which these 
plates are annexed, whose name is not mentioned, takes some 
pains to refute the opinion of M. Reaumur, who calls the 
surfaces of the soles of the fly’s feet p.elotes , or balls, which 
this author ascribes to M. Reaumur not having seen them, 
sufficiently distinctly. This author says, that they are not balls, 
MDCCCXVI. X 
