186 BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



ing and in the detailed measurements of many thousands of 

 individuals of different ages to ascertain in a general way the 

 requirements for persons of different ages. Meyer's statement 1 

 of principles is as follows : 



"The two seat-bones are curved like a bow; a line joining the lowest 

 points of these two bones is called the seat-bones line; the center of 

 gravity of the body is in front of the ninth or tenth chest vertebra; and 

 a straight line from this point to the ground is the line of gravity. Up- 

 right sitting is possible only when this line passes through the seat- 

 bones line. This line determines the surface of support for the body. 

 But the least movement that displaces the center of gravity makes up- 

 right sitting impossible without great muscular effort. The surface of 

 support is then determined by some third point. In a forward-sitting 

 posture the line of gravity falls in front of the seat-bones line, and the 

 third point that determines the surface of support is given by the edge 

 of the form, or when the seat is not broad, by the point where the feet 

 come in contact with the floor, or by both points together. The line of 

 gravity may now fall on that surface which is determined by the front 

 edge of the seat and by the muscular effort required to keep the body 

 in equilibrium. Hence the nearer to the knee the seat extends, the 

 larger the surface of support and the easier it is to retain the equilib- 

 rium. All the demands for an upright sitting posture would now be 

 satisfied if the trunk were immovably fixed in the hip-joint, but it is 

 joined movably to the thighs; hence the upright posture can be main- 

 tained only by the work of the pelvic muscles. The muscles soon be- 

 come fatigued and the body would fall forward unless supported by 

 leaning the chest and arms against the table. 



In the backward-sitting posture, in which the line of gravity falls back 

 of the seat-bones line, the end of the coccyx is the third point which de- 

 termines the surface of support. This position has the great advantage 

 of having this third point fixed and immovable. The body with this 

 backward inclination should be supported by a back rest. This may be 

 placed against the shoulders, but then the position is a half-reclining 

 one. The lower down it is placed within certain limits the more it 

 helps in an unright posture. Placed at the upper edge of the hip-bone, 

 or back of the last vertebra, it holds the pelvis and the trunk in an up- 

 right posture. The principle then is as follows: A pupil must always 

 take those positions in sitting in which the line of gravity falls a little 

 back of the seat-bones line. The upper part of the body also must be 

 supported. It is easy to determine the kind of seat that should be used 

 in accordance with this principle." 



1 Summarized by Burnbam, op. cit., p. 40. 



