Enciclopedia Britannica; un dizionario delle arti, scienze e literatureWith generale mappe nuove e originali articoli americani da eminenti writersWith American le revisioni e aggiunte, portando ciascun volume fino a data . fthe pontili al fine di alleviare i perni dal peso di theinstrument, che sarebbe presto distruggere la loro figura il fiart cilindrico di ciascuna estremità dell'asse è supportato da un gancio fornito withriction rulli e sospesa da una leva supportati da pierand controbilanciate in modo da lasciare solo circa 10 libbre pressionesul ciascun cuscinetto. In prossimità di ogni estremità dell'asse è fissata

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The Encyclopedia britannica; a dictionary of arts, sciences, and general literatureWith new maps, and original American articles by eminent writersWith American revisions and additions, bringing each volume up to date . fthe piers In order to relieve the pivots from the weight of theinstrument, which would soon destroy their figure, the cylindrical fiart of each end of the axis is supported by a hook supplied withriction rollers, and suspended from a lever supported by the pierand counterbalanced so as to leave only about 10 pounds pressureon each bearing. Near each end of the axis is attached a circle orwheel (generally of 3 or 3J feet diameter) finely divided to 2 or 5on a slip of silver let into the face of the circle near the circum-ference. The graduation is read oflf by means of microscopes, generally four for each circle at 90* from each other, as by taking themean of the four readings the eccentricity and to a great extent theaccidental errors of graduation are eliminated. In the earlier instru-ments by Pistor and Mar- wards they let the piers betins the microscopes were tSj made narrower, so that thefixed in holes drilled ^^ microscopes could be at the through the pier, but after- attached to. Transit Circlet radial arms starting from near the bearings of the axis. Thisis preferable, as it allows of the temporary attachment of auxil-iary microscopes for the purpose of investigating the errors offraduation of tho circle, but the plan of the Repsoids and ofimms, to make the piers short and to let the microscopes andsupports of the axis be carried by an iron framework, is betterstill, as no part of the circle is exposed to radiation from the pier, which may cause strain and thereby change the angular distancebetween various parts of the circle. Each microscope is furnishedwith a micrometer screw, which moves a frame carrying a cross, or ^ This instrument differs in many particulars from others : theimportant principfe of symmetry in all the parts (scrupulouslyfo

Parole chiave associate all'immagine

• bookcentury1800
• bookdecade1890
• bookidencyclopedia
• bookyear1892