MASTS, YARDS, AND ENGINE-BEAMS. 



25 



have used nothing else for a very long time, and the drawing 

 of the Porcupine quill which is here given at Fig. A was 

 made from a small piece cut from the top of the penholder 

 which I have used for some fifteen years, and with which all 

 my largest and most important works were written, including 

 the large " Natural History/' " Homes without Hands," " Man 

 and Beast," &c, &c. A portion of the same quill is also shown 

 of its real size. 



If the reader will cut a Porcupine quill at right angles, 

 make a thin section of it, and place it under the microscope, or 

 even under an ordinary pocket lens, he will see that the 

 exterior is composed of a very thin layer of horny matter, 

 and the interior filled with a vast number of tiny cells, which 

 are formed much on the same plan as the pith of elder and 

 other plants. The analogies of the pith will be treated in 

 another page. 



But were the quill merely a hollow tube filled with pith, it 

 would be too weak to resist the strain to which it is often 



PORTION OF PORCUPINE QUILL. 



SECTION OF ENGINE BEAK. 



COMPLETE QUILL. 



IRON YARD AND YARD -ARM. 



ENGINE BEAM. 



SECTION OF PORCUPINE QUILL MAGNIFIED. 



SECTION OF IRON MAST. 



liable. Consequently it is strengthened by a number of inter- 

 nal ribs, composed of the same horny material as the outer coat, 

 and arranged in exactly the same way as those of the mast. 



There are yet other points in the structure of the Porcupine 

 quill which might be imitated with advantage in the mast. 

 In the first place, the internal ribs are much more numerous 



