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THE POPULAR SCIENCE MONTHLY 



Fig. 4. 



While in the foregoing examples special stress was put on the rela- 

 tive identity of mechanical principles in engineering and nature, it will, 

 in the next place, be interesting to show that in many cases the laws of 

 rational construction and design are at a glance geometrically apparent. 



If we think of the cross-section of a tree, further growth must 

 necessarily occur in directions normal to the surface of the last year- 

 ring. This causes the year-rings and pith-rays to form a system of 

 orthogonal trajectories. In Fig. 4 such a system, consisting of two 

 conjugate pencils of circles, is shown, and is caused by a rate of growth 

 greater in one direction than another. 



The inner yellow portion of a daisy (Chrysanthemum leucanthe- 

 iii urn) exhibits a beautiful geometrical arrangement of its elements. 

 By the mathematical principle of conformal transformations it can 



