6.121 The propositions of logic demonstrate the logical properties of propositions, by combining them into propositions that say nothing [nichtssagenden Sätzen].

One could also call this method a null method. In a logical proposition, propositions are brought into equilibrium with one another and the state of equilibrium then shows how these propositions must be logically constituted.

By combining propositions into tautologies and contradictions, we show how tautologies and contradictions are made, and that such combinations do indeed produce nothing but tautologies and contradictions. Such is philosophy. Dictionary.com defines a null method thus: Zero method (Physics), a method of comparing, or measuring, forces, electric currents, etc., by so opposing them that the pointer of an indicating apparatus, or the needle of a galvanometer, remains at, or is brought to, zero, as contrasted with methods in which the deflection is observed directly; -- called also null method. The Letters to Ogden, p. 34, confirm that this is the sense Wittgenstein has in mind here.