172 CATALOGUE. PHILOSOPHY AND ARTS, PEACTICAL MECHANICS. 



pounds, and ■ 



■ of the weight, and the tarred rope, of 



3.3 pounds and — - of the weight. 

 10.34 



These results were confirmed by experiments on a roller 



allowed to move on a horizontal plane, while a rope was 



coiled completely round it. Here it becomes necessary 



to make an allowance for the friction of the roller on 



the plane, which varies as its weight, and inversely as 



its diameter. For a roller of guaiacum or lignum vitae, 



1 



8.8 inches in diameter, moving' on oak, it was of the 



Weight ; for a roller of elm |- more. 



Mr. Coulomb proceeds to relate experiments made imme- 

 diately on a simple pulley, where the fiiction of the axis and 

 the rigidity of the rope produce a joint resistance. When 



guaiacum moved on iron, the friction was — or— of 



5.4 6.4 



the weight in all velocities, besides the rigidity of the rope ; 

 the mean was — , or, with a small weight, a little greater. 



For axes of iron on copper — or , where the velocity was 



11 11.5 



small : the friction being always a litde less than for plane 



1 

 surfaces. With grease, the friction was about — . 



7.5 



With an axis of green oak, or ilex, and a pulley of guaia- 

 cum, the friction with tallow was — '; without it-L ; with 



ae 17 



a pulley of elm, these quantities became 1- 3, i. An 



33 20 



axis of box, with a pulley of guaiacum, 'gave i. and — . 



23 14 ' 



•with a pulley of elm, — and J.. An axis of iron, and a 

 29 20 



pulley of guaiacum gave, with tallow, _L. 



20 



The velocity had little effect on the rigidity of ropes, ex- 

 cept to increase the resistance slightly, when the pressure 

 was small. 



Mr. Coulomb suggests that the lower surface of a dray 

 ought to be a little convex, in order to facilitate a slight agi- 

 tation, and to diminish the friction. For launching ships, 

 he recommends oak sliding on elm, previously well 

 rubbed with tallow, by means of heavy weights ; and ob- 

 serves that the velocity ought not to be so great as to melt 

 the tallow. 



In the pulley, the friction on the axis is somewhat modi- 

 fied by the simation of the surface of contact, which is not 

 perfectly horizontal, but the difference may be neglected 



in practice. This excellent memoir is concluded by a cal- 

 culation of the force requisite to raise 8O00 pounds by a 

 capstan, and a rope of 120 strands, with a purchase of 12 to 

 1 ; and it appears, by inferences from the experiments al- 

 ready stated, that about one ninth of the force employed 

 would in this case be lost. 



Architecture in General. 



Vitruvius. 



Vitruve par Perrault. f. Par. ] 673. 



Newton's Vitruvius. 2 v. f. R. S. 



Palladio. i. 1721. R.I. 



Pli. tr. Abr. I. viii. 588. VI. viii. 4Go. 



Blondel's resolution of the four principal 

 problems of architecture. A. P. V. ii. 1. 



Aldriclis elements of civil architecture. 8. 

 Oxf. 1789. 



Krafft's theory of the orders of architecture. 

 C. Petr.XI. 288. 



Nollet's observations on architecture in Italy. 

 A. P. 1749. 473. H. 15. 



Emerson's mechanics. 



Emerson's miscellanies, 322. 



Vitruvius Britannicus. 3 v. f. Continued. 2 v. 

 f. London. 



Kent's Inigo Jones, f. 1770. R. I. 



Pini dialoghi dell' architettura. 4. Milan, 

 1770. R. S. 



Huths biirgerliche baukiinst. 



*Coulomb's application of the rules of max- 

 ima and minima to problems of architec- 

 ture. S. E. 1773. 343. 



E. M. Architecturo, 1^ vol. to Es. R. I. 



Chambers on civil architecture, f. 1791. 

 R. I. 



Rudiments of antient architecture. London. 



Essai/s on Gothic architecture. 8. London. 

 R.I. 



S<?/ar/'s ruins of Athens, f. London. R.I. 



P. Nicholson's student's instructor. 8. Lond. 

 R. L 



