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Journal Of Natural Philosophy Chemistry And The Arts (Newspaper) - June 1, 1799, London, Middlesex Dffcnptiott of a 99 By this if I have not verified I have at leaft preferved MJY Whitehurfts ftandard for the I fliall confider this meafure of the difference of the length of the two vibrating 42 and 84 times in a minute of mean as On this prefumption I fliall proceed to the examination of From the opinion of different Mful perfons with whom I have as wellas from the refult of my own I am inclined to there is hardly any body in nature with which we are familiarly that is of fo fimple and homogenous a quality as pure diftilled or fo fit for the purpofes of this enquiry and I have that if the weight of any quantity of water whole bulk had been previoufly meafured by the abpvementioned could be attained under a known preflure and temperature of the we fhould be in pofleffion of a general ftandard of With this I directed Troughton to in addition to the very fenfible hydroftatic balance before a folid cube of whofc fides were 5 inches and alfo a cylinder of the fame 4 inches in diameter and 6 From Thomass by favour of I procured 3 gallons of diftilled water with thefe I made the following obfervations but before I relate the I will defcribe the Whitehurfts machine for meafuring the has been fufficiently explained in his pamphlet mentioned above my divided which was anew inftrumentjwas as follows Description of the or Dhidedfcak of equal ab Plate is a block or beam of 6 feet 3 inches 6 inches and 5 upon which are laid two brafs c d e andfgy each divided into 60 inches and The former of called the is for a time kept immoveablc by the fingerfcrews c e and is furnifhed with fine hairline intended to be viewed only by the b i the called the has no motion but by means of the fcrew and bears ftronger divifions upon with which the Gliding pieces or indexes at k and m may readily be compared by the naked and is intended only to fet the of rather the wires in their to the required diftance to within or of an The microfcopes are and fimilar to thofe defcribed by the JateGeneral Roy in his account of his large See The one at only crofswires fixed in its focus the other at i has a micrometer by means of 5which its crofswires may be moved to the right or or over the image of the divifions of the any given fpace not exceeding inch and the quantity fo moved may be meafured by the divifions on the fcrewhead paffing under the index at The divifions on have been called inches and tenths it was not neceflary that they fhould be more than ejual bafts but they were in fea hid down by Troughton from a fcale of the late excellent artift who had divided into inches feveral fcales of different lengths One 42 inches belonged to the late General Roy a of 5 was I do not here mean to infer any opinion refpefting the compreffibility of but only to that where water or any tiling elfe is weighed in the denfity of that as hewn by the barometer and rauft be known in order to make allowances for it if O 2 purchafed
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