"Of all the cases which come before the Court for its decision, none can be more embarrassing and more unsatisfactory than those which arise upon the construction of wills. The Court has no real guide to enable it to arrive at a conclusion. The only things which can be called guides are certain rules which the Court has laid down, and which may be extracted from the decisions. Beyond that, the decisions are not of the slightest use. Except by adherence to those rules, there is nothing but what may, not irreverently, be called guessing as to what the words of the document can be held to mean."