194 NATURE'S TEACHINGS. 



building in Bermondscy. Sometimes a transverse stay con- 

 nects the centres of the two curved beams ; but it is seldom 

 needed. 



The reader will see that if the interval between the curved 

 beams were to be filled up, we should obtain a form very like 

 that of the engine beam described in page 25 ; while, if we 

 could imagine two such girders intersecting each other at right 

 angles throughout their length, a section of the two would 

 exactly resemble the section of the engine beam as given in 

 the uppermost figure in page 25. 



IN the human body there are four admirable examples of 

 the natural Girder, namely, in the bones of the arms and legs. 



On the left hand of the illustration are shown the two bones 

 of the fore-arm, technically named the " radius " and " ulna." 

 It will be seen that these bones are arranged on the principle 

 of the girder. In men who are especially powerful of grasp, 

 it has been noticed that the curve of the radius and ulna has 

 been exceptionally bold, while we have it developed to the 

 greatest extent in the fore- arm of the Gorilla, an animal whose 

 arms are simply gigantic. 



The two bones of the legs, from the knee to the ankle, are 

 arranged in a similar manner, and are called the " tibia " and 

 "fibula." The last named signifies a brooch, and is given to 

 the bone because it is very slender, nearly straight, and when 

 in its place bears no small resemblance to the pin of the fibula, 

 or ancient Roman brooch. 



Nature, however, has exceeded Art in her girder. Those of 

 man's manufacture can only exert their strength in one direc- 

 tion, and would be of little use if force were to be applied to 

 them in any other direction. Those of the human body, how- 

 ever, have the capability of partial revolution on each other at 

 their points of junction, thus enabling the Girder to apportion 

 its strength according to the direction of the resistance which 

 it has to overcome. 



WE now come to the Tics, i.e. those internal beams, whether 

 of metal, wood, stone, or brick, which prevent walls from falling 

 outwards. There is no danger of the walls falling inward, but 

 there is very great danger of their falling outward, especially 



