that may le made of short Pieces of Timler. 349 



formation. For other uses, where expedition is of less importance, 

 it will be easy to place the frames in the position desired. 



It may not be amiss to point out a case or two in civil life 

 where the combination may be useful. In scaffolding, where in- 

 termediate supports cannot be applied from the nature of the si- 

 tuation ; in temporary bridges ; also to roofs and other parts of 

 temporary buildings, or erections. Let us suppose that a large 

 room is to be erected for any purpese. If it were 60 feet wide, it 

 rnighi be covered, with the help of the method now pointed out, 

 in a very short time, and almost without waste of materials ; be- 

 sides the advantage of employing short pieces, almost without 

 preparation, it merely being necessary that there should be some 

 pieces of the same depth. 



In conclusion : I shall make a few observations on the principles 

 which were kept in view in contriving this combination of tim- 

 bers. In the first place, it is well knowlr to those who have con- 

 sidered the nature of beams of equal resistance, that v/hen a solid 

 beam, supported at its ends, is acted upon by a moving load, its 

 vertical section in the direction of its length is an ellipse, when it 

 is equally strong at every point. The combination above de- 

 scribed was intended to approach as nearly to that form as a 

 necessary attention to other circumstances would admit. Those 

 v.'ho have not had occasion to study this part of mathematical 

 science, may most likely have observed that a beam may be much 

 reduced towards the points of support without impairing its 

 strength. 



Secondly. When a beam, resting upon distant supports, is 

 strained by a load upon any part of it, the fibres at the middle 

 of its depth are not strained in a sensible degree ; the strain be- 

 ing greatest at the upper and lower sides, and decreasing to no- 

 thing in the middle. Hence the middle part may be removed 

 without materially lessening the strength, at the same time the 

 load upon the beam is much lessened. Thus, combining strength 

 and lightness, the stems of the reed and many other plants owe 

 their strength to the same principle. And a still more striking 

 example is exhibited in the bones and wings of the feathered 

 tribe. It is one of those remarkable cases, where through science 

 we seem to look into tlie process of nature : but how clumsy are 

 our attempts to imitate her works! — Nevertheless it is always 

 possible to gain much by a due attention to phaenomena which 

 are dailv before us; and as our knowledge increases, the more we 

 find to admire — to imitate — even our own want of skill must of- 

 ten increase our veneration for Him, whose works fill our minds 

 with awe and astonisiiment. 



Civius. 



LX. Me- 



