Read this line from frankenstein: if, . . my father had taken the pains to explain to me that the principles of agrippa had been entirely exploded and that . . the powers of [agrippa] were chimerical, . . i should certainly have thrown agrippa aside. . a chimera is a deception or fantasy of the mind. why does the author use the word chimerical here?

The author Mary Shelley use the word chimerical in that line because she said that the powers of Cornelius Agrippa were improbable and because she wanted to say this in a fancy way. 

Hope this Helps :)

BTW, Mary Shelley is the author of Frankenstein 

It shows he knows real life experiences and how people live on these harsh conditions

The main themes of the play are: fate and free will with the inevitability of oracular predictions is a theme that often occurs in greek tragedies the conflict between the individual and the state similar to that in sophocles’ “antigone” and   people’s willingness to ignore painful truths both oedipus and jocasta clutch at unlikely details in order to avoiding facing up to the inceasingly apparent truth and sight and blindness the irony that the blind seer tiresius can actually “see” more clearly than the supposedly clear-eyed oedipus, who is in reality blind to the truth about his origins and his inadvertent crimes.