Why, the cunning worker had foreseen to the ridicule of my own confessed stupidity that in order to effectually bar the exposed side of the chamber it must of necessity select girders of successively increasing length and size. Thus, as I fancied it reasoned, a short stick would not span the top of the dangerous gap; while, on the other hand, a long stick could not be used at the bottom because it would strike smack against the side walls before it could be placed in position low enough. So all this clearly explained why the bird should exercise such studied care in selecting the large “timbers.” A few days afterwards I visited the scene of operations again, and by using an opera glass found that the nest was very nearly if not quite finished. The menacing gap in the ledge no longer existed; for there was a solid bulkhead in its stead composed of longitudinal sticks tied and stiffened by interwoven bits of dry grass and such shreds of various waste material as only bird intelligence knows where to find. More interested now than ever, I took pains to climb into the attic of the three story building where from a narrow gable window I could look obliquely down into the pretty nest now neatly lined with tiny feathers and thistle down. So much, then, for the sparrows and their house building. I say sparrows now, for during my later observations I had seen both Mr. and Mrs. Sparrow diligently working together. But to advert now to our alleged “libel” on the birds, I have only to say that it is very convenient for great men and ponderous books to tell us that the lower animals perform their actions by means of a tendency called “instinct;” and thus divest themselves of all further responsibility in the matter. Confronted by this obscure declaration we are led as pupils in natural history to ask, “What is instinct?” The following definitions of this much-abused term are, perhaps, the best to be found in the English language: “Instinct is a propensity prior to experience and independent of instruction.”—William Paley. “Instinct is a blind tendency to some mode of action, independent of any consideration on the part of the agent, of the end to which the action leads.”—Richard Whately. “Instinct is an agent which performs blindly and ignorantly a work of intelligence and knowledge.”—Sir William Hamilton. Now such names as Paley, Whately and Hamilton stand high upon the roll of honor in the sparkling literature of our language; and yet the words of these great scholars are but as sounding brass and a tinkling cymbal when they undertake to tell us what is the real import and inwardness of that occult and wonderful faculty in the mental essence of animals which scientists by force of circumstances have agreed to call “instinct.”