For some kinds of birds we can build houses. Some of the many forms which can be used are shown in the pictures at the end of this Leaflet. Any ingenious boy can suggest a dozen other patterns. Although birds may not appreciate architecture, it is well to make the houses neat and tasty by taking pains to have the proportions correct. The floor space in each compartment should be not less than five by six inches, and six by six or six by eight may be better. By cutting the boards in multiples of these numbers, one can easily make a house with several compartments; for there are some birds, as martins, tree swallows, and pigeons that like to live in families or colonies. The size of the doorway is important. It should be just large enough to admit the bird. A larger opening not only looks bad, but it exposes the inhabitants to dangers of cats and other enemies. Birds which build in houses, aside from doves and pigeons, are bluebirds, wrens, tree-swallows, martins, and sometimes the chickadees. For the wren and the chickadee the opening should be an inch augur hole, and for the others it should be about one-and-a-half inches. Only one opening should be provided for each house or compartment. A perch or door-step should be provided just below each door. It is here that the birds often stop to arrange their toilets; and when the mistress is busy with domestic affairs indoors the male-bird often sits outside and entertains her with the latest neighborhood gossip. These houses should be placed on poles or on buildings in somewhat secluded places. Martins and tree-swallows like to build their nests twenty-five feet or more above the ground, but the other birds usually prefer an elevation less than twelve feet. Newly made houses, and particularly newly painted ones, do not often attract the birds. But if the birds and I are companions I must know them more intimately. Merely building houses for them is not enough. I want to know live and happy birds, not dead ones. We are not to know them, then, by catching them, or stuffing them, or collecting their eggs. Persons who make a business of studying birds may shoot birds now and then, and collect their eggs. But these persons are scientists and they are grown-up people. They are trying to add to the sum of human knowledge, while we want to know birds just because we want to. But even scientists do not take specimens recklessly. They do not rob nests. They do not kill brooding birds. They do not make collections merely for the sake of making them; and even their collections are less valuable than a knowledge of the bird as it lives and flies and sings.