IN choosing wall papers for the different rooms of the house, it is not necessary to trust to guesswork and inspiration, or to the advice of the Sunday Supplement and the Ladies' Page of the Evening Magnifier. There are guiding principles which, though sufficiently general to leave much room for individual taste, are yet sufficiently definite to prevent gross error.

It is obvious that the treatment of a dining-room should be different from that of the chamber. It is clear that the upper floors of the house which receive more outdoor light, are easier to illuminate brightly in the daytime than those on the first floor or in the basement. But the situation is complicated by the fact that we must consider artificial as well as natural lighting.

To illuminate even a small room the walls and ceiling of which are dark, is practically impossible. It can be accomplished only by multiplying three or four times the amount of light used, and by enclosing the light sources in opal or other globes that vastly increase the amount of illuminating surface, and by distributing the light sources so completely that no part of the room is far from one of them.

The effect of dark walls cannot be overcome by the use of refractors that send the light down, thus insuring high photometric tests. There is no more wasteful way of distributing light than to direct it toward the floor. If the floor is dark all the light is eaten up that reaches it. If the floor is light it is slippery to walk on and disagreeable to look at. One reason why rugs, particularly pile rugs, are so satisfactory, is that they swallow up the light that does descend and give a firm foothold. The highly waxed parquet floor, unfigured and uncovered, is almost as unsafe as clear ice.

Fortunately, the majority of wall papers are comparatively light in color. Whether by day or by night, they reflect a generous proportion of the light. If they are light in color, free of surface and plain of design, the walls do all that can be done to illuminate an interior cheerfully and inexpensively.

The use of a room has everything to do with the wall paper. If the room is used mostly by day, the wall paper should be chosen with that in mind, and may be much darker than if the room is used principally by artificial light. But in natural lighting as well as in artificial lighting, strong contrasts of light and shade must be avoided. If an interior is long and narrow, with windows at ends only, or at only one end, the wall paper must be luminous with grays and golds, and free from complicated patterns.

In the living-room, that has external light on at least three sides, a comparatively dark color scheme is permissible. But in the living-room that receives little light from the sky, the wall paper must be light or the interior will be gloomy.

The shape of a room can be completely transformed by the kind of wall paper that is selected. If the room is too low, stripes or small figures and dark colors will push the walls in, while light ceiling paper in plain ivory, cream or gold will send the ceiling up. If the room is too high, it can be lowered by using a frieze wainscot or dado with filling paper that is un-figured and light in color. The ceiling should, of course, be darker than usual, and if figured with a small pattern, will be made to appear much lower.

To panel a room or to use a picture frieze or a figured ceiling paper, because it happens to be the fashion, or because the lady of the house is moved by momentary fancy, is absurd. The size and shape of the room and the size and shape of the windows absolutely control the situation. And if the room is to be used as a reception-room of any type, drawing-room, or parlor, or sitting-room, or living-room, the position of the lighting fixtures must always be considered.

As the dining-room does not need to be lighted brilliantly, darker colors in wall paper as well as draperies are often preferable. In libraries that are used for studying and seldom for entertainment, the darker colors are also permissible. In dens that are intended to be always dimly lighted, dark wall papers are permissible.

The walls of the hall should never be dark. If the hall is long and narrow and high, the ceiling should be brought down, the side walls should be spread out, and the amount of light increased whenever practicable.

People generally are more fortunate in their selection of wall papers for chambers than for other rooms. It has been the custom to employ cheerful florals in light tones. But there are many small chambers, the wall paper for which is too elaborately patterned, and many large rooms the wall paper of which has not pattern enough.

Other things being equal, walls tend to recede from the eye when hung with paper that is smooth, or unpatterned, or large-figured, or light in color. They tend to advance when rough of service or heavily patterned, especially with small figures, or in dark colors.

Of all the colors golds and yellows are the most luminous, and to them the term bright particularly applies. Nearly all the luminosity of the spectrum is to be found in yellow and its two neighbors, green and orange. It is possible to eliminate red and blue entirely without appreciably lessening the amount of light in white that is the union of all colors. But if we eliminate yellow, green and orange, there will be little light left. All red rooms and all blue rooms, even though the red has been grayed and the blue has been overpowered with white, are expensive to light.

The colors in the middle of the spectrum are also the easiest to see by. They are better adapted to the human eye. They represent the average wave-length, which almost all persons can see with equal distinctness. At the red end of the spectrum, the eyes of many are color blind. At the blue end of the spectrum, the eyes of others are keen.

The woodwork and furniture of the room should be taken into consideration in selecting the wall paper. If the doors, windows, sideboards and cabinets are many and large, the use of plain or small diapered patterns on the side wall is imperative. To spread huge Renaissance pomegranates and florals over a surface that is much broken mutilates them disagreeably. To use wall paper that contrasts violently in color with the woodwork and furniture is also disagreeable. Dark furniture in a room with light walls is as obtrusive as is light furniture in a room with dark walls.

Simplicity is the only safe principle. But this does not necessarily mean muslin curtains and absence of ornament. It means absence of mixture and absence of violent contrasts. It means that when furnishing an inexpensive Colonial interior, you do not introduce the grandiosity of Louis XIV. It also means that when you are doing a dainty boudoir after the fashion of Louis XV, you should employ the colors and shades that were rightly employed in the Eighteenth Century, because they went well together. Undoubtedly any assemblage of furnishings that accomplishes harmony is deco-ratively good, even though founded not on period style.

The trouble is that few of the masters as well as few of the laymen are sufficiently familiar with the principles of decoration, and have senses sufficiently keen to color, and line, and mass, to originate anything that is really good. Even in Germany and Austria, where straight lines and squares and rectangles are being manipulated with such wonderful success, failures are frequent. And as for the French Art Nouveau that flourished at Nancy and Paris a few years ago, its sinuous stems and parabolic curves have long since uncoiled themselves into nothingness.