Attention is not a faculty of the mind in the same sense as perception, abstraction, judgment, etc., but is rather in the nature of an act of will concerned in the focusing of the consciousness upon some object of thought presented or represented to the mind. In some respects it bears a resemblance to Abstraction, inasmuch as it sets aside some particular object for the consideration of the consciousness, to the exclusion of other objects. Wayland explains attention as a condition of mind in which the consciousness is excited and directed by an act of the will. Hamilton says: "Consciousness may be compared to a telescope; Attention is the pulling out and pressing in of the tubes in accommodating the focus of the eye;" and also that: "An act of attention, that is an act of concentration, seems thus necessary to every exertion of consciousness, as a certain contraction of the pupil is requisite to every exertion of vision.... Attention then is to consciousness what the contraction of the pupil is to sight, or to the eye of the mind what the microscope or telescope is to the bodily eye.... It constitutes the better half of all intellectual power." Brodie says that: "It is Attention, much more than any difference in the abstract power of reasoning, which constitutes the vast difference which exists between minds of different individuals." Butler says: "The most important intellectual habit that I know of is the habit of attending exclusively to the matter in hand.... It is commonly said that genius cannot be infused by education, yet this power of concentrated attention, which belongs as a part of his gift to every great discoverer, is unquestionably capable of almost indefinite augmentation by resolute practice." And Beattie says: "The force wherewith anything strikes the mind is generally in proportion to the degree of attention bestowed upon it."