LAWS OF BONE ARCHITECTURE 217 



the misinterpretation of the true significance of the inner struc- 

 ture by many others. 



The basis of a mathematical analysis of the femur 



Freiberg ('02) has urged that to establish a satisfactory 

 mathematical proof of the mechanics of the femur "we must 

 know every possible stress to which the bone is to be submitted 

 under normal conditions, and these stresses must be expressed 

 in figures." This statement may appear fair and logical but 

 it demands an excessive amount of evidence. No engineering 

 structure of even the greatest magnitude would be designed in 

 accordance with the strict requirement above quoted, that every 

 possible stress must be known. In the development of any 

 structural design the object sought is to compute the maximum 

 effects of all loads to be carried by the structure, and the vari- 

 ous combinations of these forces which could be in action at one 

 time to produce maximum effects. But no attempt is made to 

 consider the effect of every possible stress. 



For example, in the design of a railroad bridge the general 

 outline or skeleton form of the structure is assumed; then the 

 stresses are computed in each part of the structure which are 

 produced by the dead weight of the sti'ucture (which must be 

 assumed), the live or moving load that produces maximum 

 effect, the weight of snow, the effect of impact due to rapidly 

 moving loads, and the force of the wind. These stresses are 

 computed separately for each factor causing stress and then the 

 maximum stresses in each part are determined by adding to- 

 gether the stresses caused by the combinations that obviously 

 can or may act simultaneously on the structure. Then each 

 part is proportioned to safely carry the maximum stresses that 

 occur in it, under the assumed conditions. 



But were we merely striving to determine if a certain struc- 

 ture were designed in accordance with the principles of me- 

 chanics the procedure would be reversed. The form of the 

 structure would be known and its dimensions in every part. 

 The stresses produced by the dead weight of the structure 



