It is natural for a young mind to like to learn, as it is for a healthy stomach to be supplied with food; but knowledge, like the food, must be fit for the use that is to be made of it and for the organ that is to receive it; and the brain, like the stomach, has a signal which it flies to show whether the food is what it wants or not. The brain exhibits interest exactly as the stomach exhibits appetite. The object of scientific education is to discover what the spontaneous, universal interest of children of certain ages is, and to meet that interest with the fullest possible supply of knowledge in every conceivable form. Scientific education does not depend upon text-books or upon merely verbal explanations, but gets the idea home to the child by the means of a varied appeal to all the senses and sensibilities. For this reason the most advanced schools have many more studies and what are commonly called accomplishments than the public or parochial schools. That is, they add to the three r's--reading, 'riting and 'rithmetic--drawing, modeling, painting, manual training, physical culture, dramatic representation, music, field trips, and laboratory work. [Sidenote: Correlation of Studies] Yet this apparently great increase of subjects in the number of studies actually lessens the amount of work required of the child, because all these different activities, by means of what is called correlation, are brought to bear upon the same subject. For example, the class which goes out for a field trip to visit a near-by brook sees the water actually at work, cutting its way to the river, and thence to the sea. They measure its force and note its effects; they make a water-color sketch of some curve of it; they notice what birds and insects are about; what flowers grow there; what indications there may be of burrowing animals. When they get back to school they model, perhaps, some bird that they have noticed; or in the geographical laboratory, with streams of water try to reproduce in miniature the action of the brook upon the soil through which it flows. For their arithmetic lesson they estimate the number of years the brook must have been flowing to have cut its valley to its present depth. They make a full report and description of their day's work for their reading and writing lesson. They have thus gained an immense amount of information, and have done a great deal of hard work; but instead of being nervously exhausted, they are bright and exhilarated. Such fatigue as they know is wholesome and fits them for a sound night's sleep. [Sidenote: Home Expedients]