Item 125 - Letter from Augustus De Morgan

7 Camden St. and Town - Apologises for not thanking Whewell earlier for a copy of his polemic with Henry Mansel. He has been stimulated by a mathematical axiom: one of his pupils has found that he never has to use more than four colours when drawing countries which have a common boundary line. He is preparing a paper on algebra in which it is 'distinguished into 'formal' and 'material' - and this is much connected with the same view of logic'. William Hamilton claims that 'a proposition, as to logical import - nothing but an equation or non-equation between the quantities of its term - merely - and the coalescence of two terms into one notion is a consequence ('consequent upon') of the equation. To my untutored mind, it is the other way - declaration of coalescence - followed by equation of quantity for a consequence'.