138 LECTURE XVI. 



must not be too rapid, otherwise the resistance of the air will destroy too 

 much of the motion ; but in the kitchen jack, as well as in the striking 

 part of a clock, where the superfluous force is purposely destroyed, the fly 

 is made light, and strikes the air with a broad surface. An effect similar 

 to that of a fly and a spring is sometimes produced in hydraulic machines 

 by the introduction of an air vessel, the air contained in which is com- 

 pressed more or less according to the intensity of the force, and exerts a 

 more uniform pressure in expelling the fluid which is forced irregularly 

 into it. 



LECT. XV. ADDITIONAL AUTHORITIES. 



Lahire's Mech. Par. 1695. Maudey's Mechanical Powers, 1709. Leupold, Thea- 

 trum Machinarum, 9 vols. fol. Leipz. 1724. . . . Euler on the Theory of Machines, 

 Com. Petr. x. 67. Nov. Com. Petr. iii. 254 ; viii. 230. Hist, et Mem. de Berlin, 

 1747, 1752. Camus, Cours de Mathematiques, Par. 1766. Berthelot, Mecanique 

 appliquee aux Arts, 2 vols. 4to, 1773. Jacobsons Technologisches Worterbuch, 

 von Rosenthal, Berl. 1787. Person, Recueil de Mecanique, 4to, Paris, 1802. 

 Banks on the Power of Machines, Kendal, 1803. Guenyveau, Essai sur la Science 

 des Machines, Lyons, 1809. Lippi, Principj Pratici di Meccanica, Napoli, 1811. 

 Lauz et Betancourt, Essai sur la Composition des Machines, 4to, Par. 1819. Bprgnis, 

 Traite Complet de Mechanique appliquee aux Arts, 7 vols. 4to. Paris, 1818-20. 

 Dictionnaire de do. 4to, 1823. Hachette, Traite Elementaire des Machines, 1828. 

 Robison, art. Machinery. Coriolis, Calcul de 1'Effet des Machines, 1829. Navier, 

 Resume des Lemons donnees & 1'Ecole des Ponts et Chaussees, 1833. Prony, Me- 

 moire sur un Moyen de convertir les Mouvemens, &c. 4to, 1837. Whewell's Me- 

 chanics of Engineering, Camb. Willis's Principles of Machinery, Camb. 1841. 

 Poncelet, Introduction a la Mecanique Industrielle, Metz et Paris, 1841. Moseley, 

 The Mechanical Principles of Engineering, 1843. 



WheelworJc. Hooke's Perfection of Wheelwork. Cutlerian Lectures, No. 2, 

 Animadversions on Hevelius, 4to, 1674, p. 70. Lahire on the Teeth of Wheels, 

 Hist, et Mem. de Paris, ix. 90, 283, 292. Camus on do. ibid. 1733, p. 117, H. 

 81 ; and Cours de Mathematiques, 4 vols. translated, 1806. Euler on do. Nov. Com. 

 Petr. v. 299 ; ii.207. Ferguson's Lectures, by Brewster, 2 vols. 1806. Buchanan, 

 Essay on the Teeth of Wheels, 1808. Trans, of the Soc. of Civil Engineers, ii. 89. 



LECTURE XVI. 



ON THE UNION OF FLEXIBLE FIBRES. 



THE strength of cordage, and of other substances which are employed in 

 the communication of motion where flexibility is required, as well as the 

 utility of other flexible materials which serve for furniture or for clothing, 

 depends principally upon the lateral adhesion produced by twisting, or by 

 the intermixture of fibres. The union of flexible fibres, therefore, being 

 frequently subservient to the communication of motion, and the machinery 

 usually employed for producing it, belonging immediately to the subject 

 of the modification of motion, we may with propriety consider at'present, 



