EXPERIMENTAL MECHANICS. 



Bv ^^•. D. EGGAR. M.A. 



Mechanics is the mother of t\\o sciences, Engineer- 

 ing and Gravitational Astronom\'. This statement is 



perlia[)s open to question, 

 astronomers ma\' w isli to 



15oth engineers and 

 claim a more remote 



ancestry for their studies. r>ut, \\ ithout insisting on 

 the precise relationship of the difterent groups, we 

 may point out that Gravitational Astronomy is very 

 much younger than mechanics, 

 and it might almost be said that 

 she made lier entry into the world 

 after the manner nf Miner\'a, 

 apj>earing full grown and fulh' 

 equipped from the brain of the 

 g(_)d-like Newton The perfec- 

 tion of her equipment, and the 

 unexceptionable propriet\' of her 

 demeanour commended her to all 

 mathematicians, with the result 

 that Mechanics, her real mother, 

 was received into .their select 

 circle, taking the name of Applied 

 Mathematics, and not encouraged 

 to see much of her other daughter, 

 tond, it was feared, of low and 

 irregular company. 



Times have changed. Even 

 the House of Lords must become 

 more democratic, and engineer- 

 ing has become so \er\' much of 

 a great lad_\- as to compel 

 the respectful attitude of mathe- 

 matics, and to make her connec- 

 tion with tr.ide rather a recom- 

 mendation than otherwise. In 

 other words, tlu' world must ha\e 

 engineers, and engineers must 

 have mathematics, and, therefore, 

 mathematics has become more 

 practical. Moreover, in the 

 engineering profession itself the 

 problems which rec]uire solution 

 become more and mt^re of a kinetic 

 nature. The strains and stresses 

 in girders and embankments are as important as ever; 



Figure 1. 

 Apparatus for me.as- 

 uring time with a 



tuning fork. 



teaching of mechanics, which used to be limited to a 

 few experiments with spring balan :es and pulleys, has 

 now spread into the region of kine"'.--;. The concepts 

 of force and work are undoubtedh- " :st approached 

 by practical measurements of the efficiency of 

 simple or complex machines; and it has been 

 found that \'elocit\'. acceleration, kinetic cner^'\-. 



Figure 2. 

 Measuring tlie velocity of the rim uf a wheel. 



moment of momentum, aiul other concepts involving 

 mo\'ement can best be realized m a jiractical manner. 



Figure 3. 



but, in addition, the mechanics of movement is grow- 

 ing in importance, ^^'e move faster nowadays, not 

 only on the railways, but on the roads, in the water, 

 and even in the air. Hence it is that the practical 



Fletclier's trolley for measuring acceleration. 



The measurement of time has alwa}s been a 

 difficult}- in the way of those who have tried to teach 

 kinetics by experiment. Electric chronographs 

 are expensive, and, even where expense is no bar, 



