I74 CATALOGUE. — PHILOSOPHY AND ARTS, PRACTICAL MECHANICS. 



sections similar, the two portions must have their outlines 

 cubic parabolas. For a weight equally divided, or applied to 

 any point at pleasure, the cube of the diameter must be as 

 the square of the segments. 



A wall, turning a vertical face to the wind, ought to have 

 the other face an inclined plane, in order to resist the force 

 of the wind to the greatest advantage, if made of cohesive 

 materials ; but if of loose materials, it ought to be convex 

 and parabolic behind. Emerson. 



A cohesive wall, supporting a bank of earth or a fluid 

 with its Vertical face, ought to be concave behind, in the 

 form of a semicubical parabola, with its vertex at the top of 

 the wall : but if the materials are loose, the back of the wall 

 should be an inclined plane. Emerson. 



A pillar or column of cohesive materials, formed to resist 

 the wind, must be a cone or a pyramid ; of loose materials, 

 a parabolic conoid ; to support its own weight only, a pillar 

 must have the logarithmic curve for its outline. Emerson. 



A mortise hole should be taken out of the middle of a 

 beam, not from one side ; but if it is on the concave side, 

 and is filled Bp with hard wood, it does not diminish the 

 strength. For similar reasons, a piece spliced on, to strength- 

 en a beam, should be on the convex side. If a cylinder is 

 to be supported at two points with the least strain, the dis- 

 tance between the points should be .5858 of the length. 

 Emerson. 



If a piece be spliced on a divided beam, equal in depth 

 to half the depth of the beam, the strength is greater than 

 that of the entire beam, in the ratio of 1 to 1.054, very 

 nearly. 



Coulomb found the lateral cohesion of brick and stone 

 only jlj more than the direct cohesion, which, for stone, was 

 215 pounds for a square inch ; for good brick from 280 to 

 300. Supposing this lateral cohesion constant, a pillar will 

 support twice as much as it will suspend, and its angle of 

 rupture will be 4 5°. From the same supposition it may be 

 inferred, that the strongest form of a body of given thickness 

 for supporting a weight, is that of a circle, since the power 

 of the weight in the direction of every section varies as the 

 length of that section ; and the strength is therefore equal 

 throughovit the substance. But if the cohesion is increased, 

 like friction, by pressure, and supposing, with Amontons, 

 that this increase, for brick, is three fourths of the weight, 

 the plane of rupture of a prismatic pillar will form, accord- 

 ing to Coulomb, an angle of 63° 26' with the horizon, and 

 the strength will be doubled. On both suppositions the 

 •trength is simply as the section. It is of the less conse- 

 quence to investigate the lateral pressure of soft materials, as 

 they arc generally liable to be penetrated by water, which 

 acts according to the laws of hydrostatics. 



Particular Structures. 



Barville's turning parapets for defence. Mach. 



A. II. 23. 

 Godefroi's staircase. A. P. 1716. H. 78. 



Mach. A. III. 99. 

 Lahire on keeping out rain from windows. 



A. P. 1716. 326. 

 Beiidor on lighthouses. Arch. Hydr. II. ii. 



pi. 18. 

 Meister on the pyramids of Egypt. N. Q. 



Gott.V. 192. On fortifications. Commen- 



tat. Gott. 11. M. 20. III. 30. 52. 

 Report of a committee on prisons. A. P. 1780. 



409- H. 8. 

 Tessier on stahles. Roz. XV. 1 14. 

 *Smeulon on the Eclystone lighthouse, f. 



Lond. 1793. R. I. 

 Lighthouses. .Smeaton's reports. 

 Saunders on theatres. Vol. 1. 4. London. 

 Battham's panopticon. 

 Beatson, Hunt, Crocker, and Sinclair on 



farm buildings. Board Agr. I. 1. 

 Lord Brownlow on cottages. Board Agr. I. 8o- 

 Saillet 8ur les theatres 4. 1801. 

 Flaw's rural architecture. 4. 1802. R. I, 

 Chimnies. See pneumatic machines. 



Materials. Masonry, Biicks, Pave- 

 ments. 



See Passive Strength. Roofs. 



Fourcroy et Gallon Art du tuilier briquetier. 



f. Paris. 



Extr. A. P. 1763. H. 139. 

 Dtihaniel Art du couvreur. f. Par. 



E.xlr. A. P. 17C6. H. 156. 

 Jars on making bricks and tiles. A. P. 1768. 



H. 127. 

 ]\Iasonry. Beiidor. Arch. Hydr. I. ii. 

 Bricks. Roz. Introd. I. 433. 



