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Actually, Griffin threw some stuff around because he's just kind of an angry guy, as Kemp notes.
Kemp tells Griffin that he wants to help, but first, he needs to know his story. So strap yourself in for Griffin's story. (This is really the only time that we get a story from Griffin's point-of-view, so it's worth re-reading to see how he defends his violence and how he thinks about himself.)
Griffin was a medical student at the same time as Kemp, but Griffin switched to physics because he was interested in light. He came up with a loose theory for how to make objects invisible, but needed to figure out a method to actually do it.
(There's some pretty hilarious dialogue here, too. After Griffin gives a long comment on reflection, refraction, and absorption of light, Kemp remarks: "that is pretty plain sailing" [19.25]. If it's not plain sailing for you, you can always read up a little more on the concepts.)
Griffin left London (and University College) six years ago and went to Chesilstowe, where he was a teacher and a student. What he really wanted to do, though, was continue his research into invisibility.
Still – and this is his big problem – his professor (Oliver) was "a scientific bounder, a journalist by instinct, a thief of ideas—he was always prying!" (19.33). Griffin didn't want to publish his research because then Oliver would get a lot of credit for it.
Griffin had done all this work himself. As he notes, "In all my great moments I have been alone" (19.37).
One night, alone, Griffin figured out how to make a human invisible. Pretty soon he was thinking about making himself invisible, since it would get him out of his life as "a shabby, poverty-struck, hemmed-in demonstrator, teaching fools in a provincial college" (19.38). Harsh!
After three years of teaching and research, he didn't have the money he needed to complete his research. So he did the obvious thing: he robbed his dad.
Unfortunately, the money he stole was not actually his dad's, and so his dad shot himself.
(This is a slightly confusing part of the plot. Whose money was it originally? Why does Daddy Griffin kill himself? The story gives no answers.)