532 



to the appointment of Mr. Baily as immediate manager of the work. 

 Mr. Baily made experiments on the fitness of different alloys, and 

 fixed upon a hard bronze or gun-metal as best for the Standards. He 

 then repeated some of Rater's experiments ; made experiments on 

 the thermometrical expansion of different metals ; compared the 

 various bars on which the restoration of the Standard must depend ; 

 and proved that the Royal Astronomical Society's tubular scale was 

 not worthy of entire credit as a means of restoring the length of the 

 old Standard. Mr. Baily's death interrupted these inquiries. 

 Generally, however, it appeared that it would be very undesirable to 

 refer in any degree to Shuckburgh's scale (adopted by Kater as the 

 Scientific Standard), inasmuch as there was no security whatever 

 that, in retaining documentary or numerical expressions of measure 

 founded on this scale, we were referring to a consistent system ; that 

 the old legal Standard was, through a sensible range, indeterminate ; 

 that the new Standard must be firm in its structure ; that firm com- 

 paring-apparatus must be used, and that new thermometers must be 

 constructed. 



Section IV. records the proceedings of the Committee and of Mr. 

 Sheepshanks (who, after the death of Mr. Baily, undertook the 

 construction of the Standard of Length) to June 1847 ; the con- 

 struction of new Thermometers ; the erection of the massive Com- 

 paring Apparatus' in the cellar of the Royal Astronomical Society at 

 Somerset House, with a description of the Apparatus and of Mr. 

 Sheepshanks's method of comparing. 



Section V. describes the proceedings of Mr. Sheepshanks to the 

 middle of 1 850 ; the preparations of Thermometers ; the discussion 

 of the values of the scales compared with the old Standard ; the suc- 

 cessive adoption and rejection of "Brass 2," "Split-plug A," and 

 " Bronze 12," as Basis for the new Standard; the final adoption of 

 "Bronze 28;" experiments on thermometric expansion;, and first 

 suspicion of personal equation. 



Section VI. gives an account of the operations of important cha- 

 racter to the end of 18.53 ; comparisons of a small number of bars 

 with Bronze 28 ; investigation of personal equation ; investigation of 

 the effect of inside or outside position of the bar ; investigation of 

 the relative thermometric expansion of steel, wrought iron, cast iron, 

 copper, and brass, as compared with bronze ; trial and rejection of 



