know then that idril had a great power of piercing with her thought the darkness of the hearts of elves and men , and the glooms of the future thereto -- further even than is the common power of the kindreds of the eldalie ; therefore she spake thus on a day to tuor : `` know , my husband , that my heart misgives me for doubt of meglin , and i fear that he will bring an ill on this fair realm , though by no means may i see how or when -- yet i dread lest all that he knows of our doings and preparations become in some manner known to the foe , so that he devise a new means of whelming us , against which we have thought of no defence .