What is the origin for the idiom "fly off the handle" ?

the first proposition is to question economic materialism and victorian christianity. the lines are:

“it moves us not.—great god! i'd rather be

a pagan suckled in a creed outworn; ”

wordsworth is stating that nature no longer interests mankind, that the latter is not “moved” by it and explains that ancient western paganism had a more positive attitude concerning nature since it lacked the perv erted judaeo-christian interpretation of having received the world and all its animals and elements from god to use as we , instead of humans actually being not only part of nature but its wardens, meant to appreciate it and protect it.

the next lines are:

“so might i, standing on this pleasant lea,

have glimpses that would make me less forlorn;

have sight of proteus coming from the sea;

or hear old triton blow his wreathed horn.”

wordsworth here make it very clear that by actually looking and contemplating nature, human beings would reconnect with happiness, serenity and purpose. the use of mythological figures is quite evocative as well, proteus is a greek mythological god of the changing sea. he personifies the sea that changes, which symbolizes the way nature changes and inevitably can change to be destructive not only due to natural causes but to human pollution. furthermore, the sea is even more symbolic since all life originated in the sea so it is not only our past but our future since no life form in our planet can survive without water and if all water is destroyed in earth all life will be gone as well.

he then uses triton which is symbolic of the synthesis of both nature and mankind. triton is a mythological greek god that has the upper body of a man and the lower body of a fish (a merman). this human fish duality evokes the fact that humans are not only human but also part of nature, the fish tail representing nature. the main attribute of this god was that he used a conch shell as a horn to calm the roaring seas. in other words, triton uses nature through science for the benefit of human sailors who risk death during tempests. with the use of such metaphor, wordworth is conveying the message that human technology   is supposed to use nature to preserve nature and thereby humanity as well.