The cheap reproduction of models is the most important problem connected with the art, and the one that is attracting most attention among those engaged in it; as, until models can be reproduced cheaply, they will never have any wide distribution and there will be far less incentive to the modeler. Various materials have been suggested and experimented on, but nine-tenths of the models that are made to-day are made of plaster of Paris. Although this material was the first to be used for this purpose, it has not yet been superseded. A plaster cast is heavy, expensive and easily injured; but plaster gives an accurate copy of the original, retains permanently the form given it, and is easily finished and repaired. The weight is an obstacle that can be easily overcome. By the incorporation in the plaster of fine tow, or of bagging or netting of various kinds, the cast can be made very light and at the same time strong, but the expense is increased rather than diminished by this method. Models made in this way, however, have the advantage that when broken the pieces do not fall out, they are, however, fully as liable to surface injury as the other kind. The large cast in the National Museum, before referred to, was made in this way. It weighed nearly 2,000 pounds when boxed--not an easy thing to handle--but it stood shipment to New Orleans and back without suffering any material injury. This would hardly have been possible had the cast been made from plaster alone. Paper seems, at first sight, to be the material best adapted for the reproduction of models; but no one has succeeded well enough with it to bring it into use. Like nearly all those who have given this subject attention, I have experimented with paper, but the only positive result has been a loss of a large part of the confidence that I once had in the suitability of the material. Paper has been used extensively for large scale models of pueblos, ruins, etc., but I have never obtained a satisfactory result with subjects in low relief and fine detail. A paper cast may look well when first made, but it absorbs moisture from the atmosphere, and contracts and expands with the weather. The contraction is apt to flatten out the model and the expansion to make it buckle up.