When the Inspector is first introduced, Priestley writes, 'The Inspector need not be a big man but he creates at once an impression of massiveness, solidity and purpose'. The triplet makes clear that he will dominate proceedings from now on, despite the hostility he faces from Mr and Mrs Birling. Also the first part of the quote shows that his ability to dominate does not come from his physical stature. Neither does it come from showy dress as he wears only a 'plain darkish suit of the period'; in other words his attire is unremarkable. His ability to dominate comes from his impressive manner; this is made clear when Priestley writes 'He speaks carefully, weightily, and has a disconcerting habit of looking hard at the person he addresses before actually speaking'. The Inspector moderates his voice and also insists on eye contact to achieve maximum impact. All this and we haven't even mentioned his supremely taxing questions yet!
What should the Inspector's appearance convey to the audience?
As soon as the Inspector enters the room, Priestley describes him as 'an impression of massiveness, solidityand purposefulness.' This triplet shows that from now on, the Inspector is in charge. He has authority and the power to interrogate the characters in to spilling the beans about the sins they are responsible for. Priestley also says that he 'need not to be a big man.' This shows that he doesn't need to use his physical appearance to show his power. He could be a small man with equal power to a huge man but in this case, the power that we are looking for is not the ability to fight someone physically, but to fight their minds and making them into confessing and sharing their guilt.
Just before the Inspector arrives, Mr Birling says that clothes for a women are 'a sort of sign or token of their self respect.' This shows that in Arthur's mind, clothes play a huge part in showing off their status to gain respect and power. In this case, the Inspector is wearing a 'plain darkish suit.' He doesn't need an actual object to objectify who he really is. His charateristics have the power to make people do what he wants them to do.