(as measured between its extreme ends) to the length of the line-bars (as measured from line to line). Suppose, also, that each of the end-bars has a well sunk to the middle of its depth, with a transverse line cut upon a pin (as in the line-measures); the line being not necessarily at the middle of the length of the bar, though it is essential that its distance from the centre of the bar's length be nearly the same in both end-bars. As, generally, one segment of the bar, from the transverse line to the end, will be longer than the other segment, let the longer segment be denoted by + and the shorter by And suppose that the two bars are placed end to end, the end of one being opposed to the - end of the other. The distance between their transverse lines will evidently be the sum of the + segment of the first bar and the segment of the second bar; and the conditions stated, as to the similar division of the lengths of the two bars, will make that sum so nearly equal to the length of the line-measure, that the difference may be measured by the micrometer-apparatus. Then interchanging the positions of the end-bars, so that their other ends shall be in contact, the distance under observation will be the sum of the segment of the first bar and the + segment of the second bar. Adding together the two measured distances, we have a comparison of the sum of the two end-bars with double the length of the line-bar. In order to make this determination available, it is necessary further to determine the difference between the whole lengths of the two end-bars. A felicitous suggestion by Mr. W. Simms, jun. gave the means of doing this. Mr. W. Simms's proposal was, to apply the process above described to three end-bars, determining the measure of the sum of each pair of end-bars in reference to double the length of the line-bar; then there are given three equations to find three unknown quantities. The length of each of the three end-bars is thus found without difficulty. Mr. Sheepshanks had commenced the preparation of some end-bars, but no efficient progress was made in their completion up to the time of his decease. The Astronomer Royal, on then revising the condition of the work, requested Mr. Simms to undertake the whole operation of testing and adjusting the bars in his own workshops, and, finally, of making the definitive comparisons with Bronze 28 on Mr. Sheepshanks' apparatus at Somerset House. Section IX. Closing Proceedings of Official Character; Extracts from the Final Report of the Commission; Extracts from the Act of Parliament legalising the new Standard; Standard Temperatures for the Compared Bars; Disposal of the Bars. -The final Report of the Committee, addressed to the Lords Commissioners of Her Majesty's Treasury, was signed on the 28th of March, 1854. We can only afford room for the following extracts: "20. The expansions of these bars corresponding to a given change of temperature had been sufficiently determined in the course of the experiments; and it was then judged expedient, instead of stating the difference in the length of the selected bars at the same temperature, to infer the difference of temperature which would cause all to represent the same length, by the application of which it would be possible to assign the specific temperature at which each bar represents precisely the length of one yard. Thus it was found that the length of one yard, as given by the lost Imperial Standard, is represented with no sensible uncertainty, except in the measures of the Imperial Standard itself, by the following bars, at the temperatures placed opposite to them: Bronze 19, or No. 1, at 62.00 Fahrenheit. Bronze 2, or No. 3, at 62 10 Fahrenheit. Bronze 7, or No. 4, at 61.98 Fahrenheit. Bronze 28, or No. 6, at 62'00 Fahrenheit. "21. The degrees of temperature for the use of these standards are defined as proportional to the corresponding apparent increase of volume of quicksilver in the thermometertube; the degree 32° representing the freezing-point of water; and the degree 212° representing the temperature of steam under Laplace's standard atmospheric pressure, or the atmospheric pressure corresponding to the following number of inches in the barometric reading reduced to 32° Fahrenheit: 29*9218+0.0766 × cosine (2. latitude) +000000179 × height in feet and the degree 62° denoting the temperature which produces in the quicksilver an apparent expansion equal to of the expansion between 320 and 212°; and so in proportion for other degrees. "23. We propose that the bar No. 1 be adopted by the Legislature as the Parliamentary Standard of one yard; that Nos. 2, 3, 4, 5, be adopted as Parliamentary Copies, and that No. 6 be retained by some officer of the Government for the comparison of other bars, or for other scientific purposes in which reference to the Standard may soon be required. We will advert shortly to the proposed places of deposit of the Standards Nos. 1, 2, 3, 4, 5. * "33. Remarking this probable intention of the Legislature in the year 1760, and remarking also the evident propriety of * Reference is here made to a Bill which was introduced into Parliament in 1760, containing provisions for the safe custody of the standards of weight and measure. placing the National Standards under the care of the Executive, we recommend that the Parliamentary Standards of one yard and one pound be deposited in the office of the Exchequer, there to be preserved under such regulations as the Parliament may affirm fitting. 66 ; 34. In selecting places for the preservation of the authentic copies of the Parliamentary Standards, we have been guided by a consideration of the general fitness of the offices named by an appreciation of the careful and accurate habits of the persons employed in them; by the limited accessibility to standards preserved in such offices, which it may be presumed will be made available for their legitimate purposes only; and by the occasional utility of accurate standards in verification of the operations to which these offices are devoted. . . . We adhere to the recommendation in Article 6 of the Report of 1841, that one set of copies should be imbedded in the masonry of a public building. In the distribution of the different copies, we have been guided by trifling peculiarities in the copies themselves. 66 35. After careful consideration, we recommend, "That the copy of Length Standard No. 2, and the copy of Weight Standard, PC, No. 1, be deposited in the Royal Mint. "That the copy of Length Standard, No. 3, and the copy of Weight Standard, PC, No. 2, be transferred to the Royal Society. "That the copy of Length Standard, No. 5, and the copy of Weight Standard, PC, No. 3, be deposited in the Royal Observatory of Greenwich. "That the copy of Length Standard, No. 4, and the copy of Weight Standard, PC, No. 4, be immured in the cill of the recess on the east side of the Lower Waiting Hall in the New Palace at Westminster." On the question of referring the values of the measure and weight represented by the standards to natural elements. 66 40. After due consideration of this question, referring to the reasons explained in Chapter II. of the Report of 1841, December 21, we adhere to the recommendation contained in that chapter, and embodied in articles 1 and 2 of the same Report, that no reference be made to natural elements for the values represented by the standards. 66 41. We consider the ascertaining of the earth's dimensions and of the length of the seconds pendulum in terms of the standard of length, and of the weight of a certain volume of water in terms of the standard of weight, as philosophical determinations of the highest importance, to the prosecution of which we trust that Her Majesty's Government will always give their most liberal assistance; but we do not urge them on the Government at present as connected with the conservation of standards." The Act of Parliament for legalising the Standards of Weight and Measure received the Royal Assent on the 30th of July, 1855, the day succeeding that on which Mr. Sheepshanks was attacked by the illness of which he died. The Astronomer Royal closes his paper with the new nomenclature of the bars, and the temperatures at which they represent the British yard. He has also given a statement of their distribution. Bar, No. 6, has been retained at the Royal Observatory, as accessible representative of the National Standard. A Treatise on Navigation and Nautical Astronomy. By John Riddle, F.R.A.S., Head Master of the Nautical School, Royal Hospital, Greenwich. 8vo. Seventh Edition. London, 1859. This excellent standard work, in which theory and practice are so judiciously blended together, is too well known to require any detailed statement of its contents. The present edition is the result of a careful revision, by which the work is adapted to the best modern practice of the art of navigation. ERRATA. Page 198, for c=280°4±83, read c=280′4±8.3. for dr=(. .. .) sin2 2, read dr = ( ) sin2 2 λ. Right Ascension and North Polar Distance of the Minor Planets, from Account of the Construction of the New National Standard of Length, and of its principal Copies, by G. B. Airy, Esq., Astro- |