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440 Lunar Method of finding the Longitude defended. --Low Wheels. After quoting the latter part of the letter from our Magazine of July, p. 332, Mr. Bradley proceeds thus:- "As to the firft part of the problem (namely, finding the longitude), I fuppofe few perfons who have practifed the Lunar method have any reafon to doubt but that the computed diftances of the fun and moon, &c. to every three hours as put down in the Nautical Almanac, are very exact. It appears to me that the gentl-man is not fo well acquainted with the rules given in the Requifite Tables, or in the Nautical Almanac for 1772, for reducing the apparent diftance on the fun and moon, on account of parallax and refraction, to the true diftance, as he out to be; as he affers a very great improvement is mady by Mr. Robinfon, but has not fhewn in what refpect." Mr. Bradley then prefeed to give 160 actual obfervations of the diftances of the fun and moon's neareeft limbs, together with the altitudes of their centers, taken on the platform on the top of the Royal Academy of Portfmouth. Near 100 of thefe obfervations are difpofed into fets of 2, 3, 4, and 6 in a fet, making in all 24 fets, and the longitude of the place is derived from each fet, by Mr. Witchel's method. The moft that any one fet makes the longitude is z° 42'; the leaft is o° 52'. The true longitude is I° 6', the latitude 50° 48'. Although we cannot give all the fpecial matter in evidence, as we wifh; yet we think enough is faid to warrant Mr. Bradley's coclufion, "That fea-faring gentleman will be fufficiently enabled from hence to judge of the ufefulnefs of this method, and of what may be expected from it when accurate fextants can be obtained." Some Account of ROLLING CARTS and WAGGONS, as they are now built by James Sharp, of Leadenhallftreet, London, according to Two Acts paffed the laft Seffions of Parliament, for the Amendment and Prefervation of the public Highways and Turnpike-roads. (See the plate.) THE rollers are placed under the body of the cart or waggon, and run abreaft, or parallel, with each other. They are true cylinders of caft iron, two feet diameter, and 16 inches broad, perfectly flat, without nails, or other projection, to injure the face of the road. The infides are tilted up with ftrong plant, fo as to appear, and have the ftrength of, a folid roller; and yet are hollow in the manner of a caik. Upon a fmooth and hard furface they are drawn as eafily as narrow wheels; and it cannot be doubted but the frequent ufe of them will render the roads both fmooth and hard. The roughnefs or inequality of roads, occafioned by wheels too narrow, or broad ones not made flat, is the great caufe of refiftance to the cattle: and not friction, as fome have fuppofed: for it may be demonftrated, that, upon the generality of roads, thefe rollers have lefs friction upon the axis than larger wheels. Some perfons having objected to them on account of the lownefs of the wheels, it is neceffary to confider how far the objection is juft. It is allowed, that there are two advantages in high wheels, viz. their being levers leffening friction upon the center, while they ftand perpendicular; and their having a larger circumference. But thefe advantages are much overbalanced by inconveniences; and it may be eafily proved, that loaded carriages with low wheels will be drawn with greater eafe to the cattle, for the following reafons: Becaufe the great increafe of weigt in large wheels, when applied to heavy carriages, is of itfelf prodigious, and muft always be confidered as a part of the load, fome of them weighing from 20 to 40 hundred weigh. Becaufe, alfo, high wheels, though levers leffening friction upon the center, when they ftand perpendicularly, are alfo levers increafing friction by lateral preffure, whenever the acarriage paffes upon uneven ground. And laftley, Becaufe high wheels require greater force to pafs them over the ufual obftables of the road; the force of the animal being then applied in a horizontal direction, and great part of it loft in preffling againft the obftacle. Thefe circumftances confidered, the balance will be found in facour of low wheels, 1. Becaufe they are both lighter and ftronger. 2. Becaufe, in general, they have less friction. 3. Becaufe lefs force is required to furmount the ufual obftacles of the road, the eleevated draught being more nearly parallel to the line of afcent. 4. Becaufe the animal can really apply more ftrength to the low than high [[image]] Fig. 5. [[image]] Fig. 8. [[image]] Fig. 3. [[image]] Fig. 9. Fig. 7. [[image]] [[image]] Fig. 4. Fig. 2. [[image]] Fig. 6. [[image]] Feet Fig. 1. [[image]]
Transcription Notes:
Fig. 1. - top view of wagon
Fig. 2. - side view of wagon
Fig. 3. - rear view of wagon
Fig. 4. - rear view of wagon
Fig. 5. - horse drawn wagon
Fig. 6. - side view of cart
Fig. 7. - rear view of wagon
Fig. 8. - ox drawn wagon
Fig. 9. - ox drawn wagon
