Another of his rules is that a cylindrical rod of well-seasoned clean-grown fir of an inch circumference drawn in length will bear at its extremity 400lbs. and a spar of fir 2in. in diameter will bear about 7 tons, but not more. A well-made and carefully-kept hemp rope of one inch in circumference, will bear 1000lbs. being at its extremity.
Mr. Barlow has formed the following table as a mean resulting from experiments on the strength of direct cohesion on a square inch of the following substances:
| lbs. | |
| Box | 20,000 |
| Ash | 17,000 |
| Teak | 15,000 |
| Fir | 12,000 |
| Beech | 11,500 |
| Oak | 10,000 |
| Pear | 9,800 |
| Mahogany | 8,000 |
He also states as follows regarding the transverse strength of beams, &c. Mr. Weale thus quotes from Mr. Barlow’s essay: “The transverse strength of rectangular beams, or the resistance which they offer to fracture, is as the breadth and square of the depth; therefore, if two rectangular beams have the same depth, their strengths are to each other as their breadths, but if their breadths are the same, then their strengths are to each other as the square of their depths. The transverse strengths of square beams are as the cubes of the breadths or depths. Also in cylindrical beams the transverse strengths are as the cubes of the diameters. Thus, if a beam which is one foot broad and one foot deep support a given weight, then a beam of the same depth and two feet broad will support double the weight; but if a beam be one foot broad and two feet deep it will support four times as much as a beam one foot broad and one foot deep. If a beam one foot square support a given weight, then a beam two feet square will support eight times as much. Also a cylinder of two inches in diameter will support eight times as much as a cylinder one inch in diameter. The appended table gives data bearing on the subject.
| Teak | 2·462 | Elm | 1·013 |
| English oak | 1·672 | Pitch pine | 1·632 |
| Canadian oak | 1·766 | Red pine | 1·341 |
| Dantzic oak | 1·457 | New England fir | 1·102 |
| Adriatic | 1·383 | Riga fir | 1·108 |
| Ash | 2·026 | Mar Forest fir | 1·262 |
| Beech | 1·556 | Larch | 1·127 |
INDEX.
A.
- Abyssinian mule platforms, [345]
- Accommodation of tents, to increase, [61]
- Adaptation of hames to collars, [460]
- Admiral Belcher’s expedient for moving vessels during calms, [175]
- Adzes or axes, makeshift, [381]
- African boots, [412]
- Aguardiente, to make, [579]
- Albatross, catching, [587]
- Alligators, catching, [590]
- Securing snared fish from, [591]
- Aloe juice, extracting, [802]
- Altitudes, ascertaining, [741]
- American cordway, [324]
- Ammunition, packing, [17]
- Amphibious animals, trapping, [666]
- Anchors, [375]
- Angle at which to pitch a tent, [56]
- Animals, calls of, [679]
- Antidotes for poison, [80]
- From arrows, [620]
- Ants, locusts, and other insects and their larvæ as food, [562]
- Anvils, [193], [197]
- Aparejo, [463]
- Application of wind power to horizontal wheel, [512]
- Aps or chupatee, [544]
- Aquatic birds, traps for, [675]
- Arctic regions, hints for the, [309], [316]
- Hutting in the, [309]
- Armament, hunter’s, [655]
- Arobas waggon, [441]
- Arrest hemorrhage, [695]
- Arrow-fishing, [594]
- Trap, [657]
- Arrows, harpoon, [594]
- Artificial horizon, [29]
- And sextant, use of, [743]
- Artillery, charges for, [241]
- Artist’s materials, [22]
- Ascertaining altitudes, [741]
- Variations of the compass, [732]
- Ash cake, [549]
- Assegais, to render useless, [203]
- Attachment of straps, for sledges, [399]
- Australian bark canoe, [162]
- Axes or adzes, makeshift, [381]
- Axles, to make and repair, [215]