How he get to know which one is positive and which one is negative as stated by him that there are two types of fluid? Also tell how he thought of two fluids?
He firstly rubbed glass rod with silk and move the glass towards the light objects(paper, foil)it got attracted and then he rubbed amber with silk and the same thing happens that is attraction. From all this phenomena he was clear that if a body is charged then it will attract light objects but not the heavy object(means a body heavier than the charged body). Then he thought if a heavy body is charged then what will happen?. So he brought amber near the glass(as we know amber is little bit heavier than glass)and both are charged, here he sees attraction hence he thought if a body is heavy but charged then another charged body can show their effect of attraction but then he went to prove this using different material and the next material was two charged glass and he brought them close to each other and he found that they repel then he was astonished as it has been known electricity phenomena only show attraction not repulsion. So he this experiment with various material ( like charged glass with many other charged materials in some it shows attraction and in some repulsion). From this he was clear that there are two types of fluid, one vitreous(glass like or positive) and the other resinous(amber like or negative). He thought when a body is not charged then there are equal amount of fluid in everyone but when a body is charged then it has two kinds of charges or fluids. He thought there are two types of fluid because of attraction( which happen when there are unequal things)and repulsion( which happen when there is equal things). He told positive means excess of fluid and negative means loss of fluid. He has taken as a convention that amber is negative and glass is positive