Notices respecting New Booh, 293 



the standard 6-inch brass scale ; and of this scale to various other 

 scales as well as to the 10-foot standard bar. As there is at present 

 no legal standard of British measures, the results are provisionally 

 expressed in terms of the 10-foot iron bar. In these details we 

 see abundant reasons to justify our regret that an account of the 

 measurement was not given by the persons by whom the ope- 

 ration was actually performed, and our desire to have another base 

 measured in England, now that the experience which has been 

 gained would lead us to expect still greater precision. It appears 

 that while the measurement was proceeding two records of ob- 

 servations were kept ; these are found in many cases to differ from 

 each other, particularly in the readings of the thermometer, and 

 no means now exist of determining with certainty which of the 

 two is the correct one. All the comparisons for ascertaining the 

 relation of the 6-inch scale to the 10-foot bar made prior to 1844 

 have been discarded as unsatisfactory in some respects, and it would 

 seem that we have only very recently, if we have yet, become ac- 

 quainted with the proper manner of making experiments of such 

 extreme delicacy, and with some of the properties of matter on 

 which the results depend. Captain YoUond informs us, that 

 "during the present }'ear (1847) it has been ascertained, that if a 

 steel bar be raised to a red heat and then cooled, either gradually 

 or by immersion in v.'ater or oil, it does not return precisely to the 

 same condition as existed prior to its being heated ; it remains, in 

 fact, enlarged." 



It would be interesting to know how nearly the lengths of the 

 sides of the triangles deduced from the Lough Foyle base agree with 

 the same distances comjjuted from the bases formerly measured in 

 England with the chain ; but on this point we have not yet any direct 

 information. It appears, however, from comparisons made at South- 

 ampton of the Ordnance new standard bar with a 20-foot iron bar, 

 from which the lengths of the chains were laid off by Ramsden, that 

 ilamsden's bar exceeded two lengths of the Ordnance standard bar 

 by 192*795 divisions of the micrometer, or by '0091877 parts of an 

 inch. This amounts to rather more than a foot in five miles — an 

 error too great to be tolerated at the present time. But as other 

 errors would arise in transferring the length of the bar to the chain, 

 and that of the chain to the base, the discordance of the computed 

 distances may be less or greater than in the proportion just stated. 



The methods of computing the distances, and the longitudes, 

 latitudes, azimuths and heights of the stations, which are appended 

 to the volume, would form an aj)propriate introduction to the details 

 of the triangulation ; for their ai)pcarancc here the following reason 

 is assigned : — " The princijjal reason why the calculations for lati- 

 tudes, longitudes, &c. arc now entered on, is, that tlie formulae and 

 tables may be available for those who may require them, as they 

 are believed to be more accurate than any hitherto jjublished." It 

 is satisfactory to be put in possession of formula and tables more 

 accurate than any which previously existed ; but who the parties 

 may bo who are likely to require those in question, or to what 



