The point of the wedge is quite indefinite, the extremely diffuse light gradually fading into invisibility at a height which may range from 50° to 70° or even more, according to the keenness of the observer's vision.
While in public life Conkling always attracted attention by his abilities, his keenness and eloquence in debate, his aggressive leadership and his striking personality.
But Lynceus, whose keenness of sight was proverbial, saw Castor through the trunk and warned his brother, who thereupon slew the mortal Castor; finally, Pollux slew Lynceus, and Idas was struck by lightning (Apollodorus iii.
On the other hand, they are constantly impressed by his power of reasoning both deductively and inductively, by the subtlety and fertility of invention with which he applies analogies, by the clearness and keenness of his observation, by the fulness of matter with which his mind is stored, and by the consecutive force, the precision and distinctness of his style, when employed in the processes of scientific exposition.
Hence the aim of education was to make young people thoroughly " Greek," to fill them with the " Greek " spirit, with courage and keenness in the quest of truth, and with a devotion to all that was beautiful.