The use of seat backs began about fifty or sixty years ago. Then followed the introduction of separate seats and later, at about 1850, the separate desks and chairs were first used. Attention had also been directed to the horizontal "distance" between the back of the desk and the front of the seat. Although a "minus" distance in which the desk overhangs the seat was advocated by some, yet Barnard and Alcott believed in a zero distance, which was, however, a step in advance as compared with the former "plus" distance of several inches.

Barnard was the first to make definite measurements of children of different ages and to devise from this a scale for the height of the seat and desk. In 1863 Fahrner, of Zurich, published the first European scale. There have since been published in this country the Whitcomb and the Bobrick scales, while in Europe the Frankfort scale, published in 1885, and the scales of the Prague and Vienna Commissions, published in 1892, are the most important. Much attention has been given to the various scales according to which fixed furniture is constructed and by which adjustable furniture is fitted. Being based on different series of measurements of children of different nationalities and classes there have been considerable differences in the results. Moreover, different standards are taken as the basis from which seat height and desk height of adjustable furniture are computed, as, for example, in one scale knee height and in another total height is taken as the basis.

ATTITUDE COMMONLY ASSUMED BY WEAK-BACKED CHILDREN.

While the scales have served a very useful purpose in bringing about more accurate fitting, according to averages, they cannot, of course, compare for accuracy in special cases with individual measurements made, for instance, in the school measuring chair, devised by Dr. Hartwell, in which at one sitting all the required measurements are easily read off. In the use of individual measurements, particularly in weak children, and in children above or below the average of those of the same age, and in careful attention to the seating of such individuals, much good may be done,

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although at present the universal adoption of complete individual measurements can scarcely be expected.

At the same time that so much was being done in the development of various scales there were introduced many different kinds of adjustable furniture, both desks and chairs.

The problems of desk construction are, according to Cohn (1), to secure such a "difference" in height between the desk surface and seat that the elbow with the arm hanging naturally just reaches the desk, which brings the book at the proper distance from the eye; (2) to secure such a horizontal "distance" between

the seat and the desk that the body and head may not be inclined forward too far in order that the eyes may be near enough to the desk; (3) to have a proper slope to the desk surface. For purposes of reading the ideal slope is 45, because then the eyes can be directed downward without fatigue and without bending the head forward. Such a slope, however, is not practicable for writing, and therefore, as a compromise, a slope of from one in six to one in ten has usually been adopted.

Modern construction in all adjustable desks meets the requirements of proper height. The problem is simple because there is no need of automatic change. The need for automatic change by the scholar in the horizontal distance between the desk and seat has been met in two ways, first, by movable desk tops and second, by movable seats. Of the movable desk tops there were two types. In one the surface is divided transversely so that one part may move upon the other, usually the posterior part folding over on top of the anterior, as in the desk devised by Parow in 1865.

There are also a great variety of mechanisms by which one-half

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of the desk top slides upon the other. Some are comparatively simple, some are rather complicated, most of them, as of the folding type, are not used because of the break in the writing surface. Some obviate this difficulty by making practically the whole of the desk surface movable, leaving only a small portion at the forward edge fixed, thus approximating the type in which the whole desk

top moves.

So much weight has been attached to the importance of a movable desk top by Lorenz and Cohn, among others, that much attention has been paid to perfecting the mechanisms by which the desk top as a whole is moved.

Some of the folding and some of the sliding desks meet the third requirements of desk slope by making a change at the same time that they change the distance, so that for reading there is a positive distance with an increased and a decreased slope. The Simplex desk of Schenck deserves particular attention. In it the "distance," the "difference" and the slope are all altered automatically by a very simple mechanism. By a simple mechanism also in the modern Chandler desk the slope and the distance may be changed together or independently as the scholar wishes. A certain amount of instruction and care is, however, necessary for the

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intelligent use of a desk of this sort, which is not necessary for those of the simplest construction.

Of course in the difference in height and the horizontal distance between the seat and the desk the chair must also be considered. Thus many adjustable seats have been made at the same time that the desks were improved. It is now universally recognized, in re

gard to the chair, that the height of the seat should equal the length of the leg from the sole of the foot to the under surface of the thigh when the feet are placed squarely upon the floor and the knee is bent to a right angle. It is generally agreed that the seat surface should slope slightly from front to back so as to counteract the tendency to slide forward, but not slope so much as materially to tilt the pelvis if the child sits sidewise in the seat. The length and breadth of the seat should correspond roughly to, the dimensions of the thighs. A seat of insufficient depth can cause no particular harm. A seat of too great breadth allows, while one of too great depth compels, bad postures. The last requirement is, as stated by Hartwell, that "the seat should be provided with a back that shall support the sitter's back whether he be quiescent or actively engaged, as in writing or drawing."

Adjustment for height is a comparatively simple matter. In some cases it is secured by adjustment of the foot rest, but now all modern seats have simple adjustments in the castings.

In order to obtain an adjustment for distance from the desk several types of seat have been made. As examples, Beyer devised one in which the seat slid on its supports, Wackenroder one in which the seat slid forward and back together with its supports and Hippauf one in which the seat, by a parallelogram motion, could be moved forward and back upon its support like an in