Memoir of the late Francis Baily, Esq., F.R.S., S^c. 51 



quantity less than half a vibration out of 86,400, or in a mean 

 solar day*. 



Standard of Length. — From the pendulum to the standard 

 of length, or the fixation of the scientific unit^ the transition is 

 easy, and, in Mr. Daily's case, was unavoidable. For, being 

 once satisfied by experience of the innumerable minute circum- 

 stances on which perfect precision in these inquiries depends, 

 and finding the parliamentary enunciation of the relation be- 

 tween the conventional and natural standards nullified, as it 

 were, under his eye, he felt himself irresistibly urged to in- 

 quire how far the conventional unit itself might be depended 

 upon, and within what limits of error it might certainly be re- 

 produced in copies. His first step in this direction was to 

 obtain the most perfect possible representative of this" unit, 

 and (as the Astronomical Society was now identified with al- 

 most all his undertakings) justly considering the possession of 

 such a standai'd by that body as a thing in itself desirable, and 

 the instrument itself likely, if thoroughly well executed, to 

 become in its hands of universal scientific reference, he pro- 

 cured himself, to be named by the Council, a Committee for 

 superintending its execution, and comparing it with the most 

 authentic standards at present existing in this country. Per- 

 haps there is no subject of inquiry more perplexing, or one 

 whose investigation calls for more patience and perseverance, 

 than the detection and exact estimation of those minute 

 sources of error which influence these delicate measurements, 

 which can only be satisfactorily performed by endless repeti^ 

 tion and systematic variation of every circumstance by which 

 error can possibly be introduced. Another and peculiar 

 source of annoyance, and even vexation, consisted in the rough 

 and careless usage to which those precious instruments, on 

 which the conservation of our national units depends, had been 

 subjected in loo many instances, by which rude and ignorant 

 hands had irrecoverably marred some of those refined pro- 

 ductions of human workmanship, which ought not even to be 

 approached but with precaution, or touched but with the ut- 

 most delicacy. Few things seem to have excited Mr. Baily's 

 indignation more than the continual occurrence of evidence, 

 only too palpable, of the small respect in which these stand- 

 ards appear to have been held by those under whose pi'otec- 

 tion they had been placed, and of the violence which has been 

 repeatedly suffered to be perpetrated on them. 



* The stations of comparison are London, Maianham, Ascension, and 

 Trinidad. Taking London for a term of departure, eacli station affords a 

 ratio whose extremes (see Report, p. 86) differ only by 0"0000103, the half 

 of which multiplied by 86,400 gives 0''44446. 



