MECHANICS. 



[Lesson II. 



rather than his fault, to be an empirical mechanic : but, in the present age of cheap 

 scientific literature, those who reject the theoretical part of mechanics altogether, have 

 only themselves to blame. Dr. PJayfair, in contrasting theory and practice, thus 

 happily expresses himself: " For a long time practice, standing still in the pride of 

 empiricism, and in the ungrateful forgettulness of what science had done in its develop- 

 ment, reared upon its portal the old and vulgar adage, 'An ounce of practice is worth 

 a ton of theory.' This wretched inscription acted like a Gorgon's head, and turned to 

 stone the aspirations of science. Believe it not ; for a grain of theory if that be an 

 expression for science will, when planted, like the mustard-seed of Scripture, grow and 

 wax into the greatest of trees. The pressure and difficulties of the age, and the rapid 

 advancement of intellect in continental nations, have been the Perseus to cut off this 

 Medusa's head from the industry of England, and to fix it on the shield of Minerva, 

 who turns to stone such as still believe that science should be ignored by practice ; 

 but, reversing that shield, wisely conducts those who would go further under her 

 guidance. It is now rare to find men who openly avow, although they actually enter- 

 tain a belief in, a necessary antagonism between theory and practice. Theory is, in 

 fact, the rule, and practice its example. Theory is but the attempt to furnish an 

 intelligent explanation of that which is empirically ascertained to be true, and is always 

 useful, even when wrong. Theories are the leaves of the tree of science, drawing 

 nutriment to the parent stem while they last, and, by their fall and decay, affording 

 materials for the new leaves which are to succeed." 



Ferguson saw his father lift up the ponderous roof by means of a lever, and he tells 

 us, that he did not consider the reason, but that the fact terrified him ; however, he goes 

 on to relate, that he thought further on the matter, and inquired if the theory he had 

 built up was well founded. To his great satisfaction, he discovered that his ideas were 

 correct. How few children there are, even at double his age, that would have thought 

 further of the matter, and inquired ! Many growp-up people would have observed and 

 passed on, without considering anything about the matter ; and if they had, their false 

 pride, in all probability, would have prevented them making any inquiries. Ferguson 

 did not stop here, he commenced making experiments with levers, applying weights to 

 them in different ways, and endeavouring to prove, practically, that which he believed 

 theoretically. His experiments were successful ; and, therefore, all that he knew was 

 not like the knowledge acquired by those who make learning a labour he knew what 

 had cost him so much trouble to learn, thoroughly, theoretically, and practically. 



QUESTIONS. 



21. T. What is a LEVER? 



P. An inflexible straight bar, or rod of 

 any material, which turns on an axis, is 

 usually termed a lever. It is one of the 

 most useful and extensively employed 

 mechanical powers. 



22. T. What is the principle of the 

 lever founded on ? 



P. The theory of equilibrium, like that 

 of all mechanic powers. 



23. T. What things have we to con- 



sider as essential to the constitution of a 

 lever ? 



P. Three: 1. The power. 2. The//- 

 crum. 3. The weight. 



24. T. What do you mean by the 

 fulcrum ? 



P. It is the axis upon, or about which, 

 the lever moves, and is generally termed 

 the prop , but is technically termed ihe 

 fulcrum. 



25. T. What is the use of the lever ? 



