forming liquid, and upon the medium ; A as influenced by 
their respective and relative densities, aud B as influenced by 
variation in the attractive power of the earth. 
In order to study systematically the influence which each of 
these causes exerts, each must be varied in succession while 
the others remain constant. 
Denoting the three states of matter solid liquid and gaseous 
by the symbols S, L, G respectively ; and considering the 
symbols in the order in which they are written, to denote 
respectively, the matter from which the dropping takes place, 
the drop and the medium, we get a convenient notation. 
As we are speaking at present exclusively of liquid drops, 
L must always hold the middle place in the symbol of the 
symoolically possible variations. 
(i) (?) (3) (4) (5) (6) (7) (b) 
SLS, SLL, SLG, LLS, LLL, LLG, GLS, GLG, 
(I), (4) and (8) are physically, impossible on account of the 
superior cohesion of liquids over solids : (6), (7), (8) are 
physically impossible on account of the superior density of 
liquids over gases. 
SLL, SLG and LLL are therefore the only cases we have 
to consider. That is : 
SLL, from a solid, a liquid drops through a liquid. 
SLG, from a solid, a liquid drops through a gas. 
LLL, from a liquid, a liquid drops through a liquid. 
Of these three caies, two, SLL and LLL, are invertable : 
that is, the motion cf the crop may be either to or from the 
earth. The gravitation of the drop may be greater than and 
overcome the gravitation of the medium, the drop descends : 
or the gravitation of the medium overcomes that of the drop, 
the drop ascends. The case LLG cannot be inverted because, 
at all events at the same pressure, every known gas is lighter 
than every known liquid. 
It will be convenient to consider the case SLG first, because 
instances of it come more frequently under our notice than of 
