BEIjIPA ST 



NATURAL HISTORY & PHILOSOPHICAL SOCIETY 



SESSION 1891-92. 



Professor M. F. FitzGerald, B.A., C.E., delivered an 



Inaugural Address on 

 THE CONTRAST OF PRACTICE AND THEORY. 



In addressing the Belfast Natural History and Philosophical 

 Society on " The Contrast of Practice and Theory" the examples 

 I propose to take in hand are, the design of bridges, beams, 

 roofs, and the like, for one ; the steam engine for another ; and 

 some points in the recent development of electrical engineering 

 for a third. 



I take beams and bridges first, as being the oldest branch, I 

 suppose, almost, of practical mechanics, since even primitive 

 man, except perhaps a cave dweller, must have used beams of 

 some kind or other in some form or other to carry a roof over 

 his head, or a floor under his feet. Accumulated experience in 

 such matters as ordinary floors and roofs has since long ago 

 been amply sufficient to enable most joists and roof frames to 

 be designed without anybody troubling his head with scientific 

 mechanics at all. When the City Authority makes regulations 

 intended to keep within reasonable limits a propensity for put- 

 ting the slimmest possible floor joists in the jerriest possible 

 houses that the inspector will pass, it is neither desirable nor 

 necessary to go into elaborate calculations. Similarly, the 

 County Surveyor would not dream of applying all the forces of 

 algebra, calculus, and trigonometry to specify the proportions 

 of a two foot culvert under a country road. Such labour would 



