hence, by substitution, as before,
PQ = PQBC. (3)
Except that the formulæ look a little more complicated there is no difference whatever.
The mood Ferio is of exactly the same character as Darii or Barbara, except that it involves the use of a negative term. Take the example,
Bodies which are equally elastic in all directions do not doubly refract light;
Some crystals are bodies equally elastic in all directions; therefore, some crystals do not doubly refract light.
Assigning the letters as follows:—
A = some crystals,
B = bodies equally elastic in all directions,
C = doubly refracting light,
c = not doubly refracting light.
Our argument is of the same form as before, and may be concisely stated in one line,
A = AB = ABc.