40 EXPLANATION of an 
was illuminated by reflected light, it appeared in its na- 
tural ftate, and when illuminated by the dire& light, in its 
unnatural ftate ; for fo I call it when the bricks appear de- 
preffed and the chinks between them elevated. 
I then confidered that fince the hearth appeared in its 
natural ftate by reflected light, and in its unnatural ftate 
by direct light, only in confequence of the inverting pro- 
perty of the glafles, the appearance ought to be direQly 
the contrary when it was viewed with the naked eye. And 
accordingly I found, upon taking out both of the glaffes, 
and looking through the open tube, that the hearth ap- 
peared as perfe€tly, and as conftantly in its unnatural ftate 
by reflected light, and in its natural ftate by dire& light, as 
it had before done the reverfe through the glaffes. But it 
muft be obferved that fomething like a tube is neceflary to 
confine the fight from other adjoining objeéts, which not 
being in the fame circumftances would otherwife corre& 
the imagination. 
If we look through fuch a tube and glaffes at the hearth 
or other obje@, fuppofe a piece of chocolate, the furrows 
in it appear fo many ridges, on removing the tube they 
fink into furrows, on applying it they again rife into ridges, 
and the illufion might perhaps be repeated a thoufand 
times, without the mind being at all able to conceive the 
obje& to appear through the tube like what it really is. 
But if whilft you are looking through the tube, and the 
objet appears in its unnatural ftate, that is, when its fur- 
rows appear ridges, you apply your finger and feel that 
they really are furrows, the deception vanifhes in a mo- 
ment and the object appears in its natural ftate. This I 
at firft fuppofed to arife from the fuperior confidence which 
we have in the fenfe of touching, as knowing by experi- 
ence that this fenfe more perfectly reprefents the figure of 
bodies than the fight does. But I was, at leaft in part, 
miftaken. For if whilft you’ fee the obje& in its unnatu- 
ral flate, another perfon puts his finger to the part you are 
looking 
