METHOD OF OBSERVING TRANSITS. 23 



/lar's centre cannot be exactly known, which makes the intro- 

 duaion of fine wires very defirable. The finefl wires ftill Spider's webs in 

 proving too thick for very fmall ftars, an aftronomical friend f 

 of mine hinted to Mr. Troughton that he might probably re- 

 ceive affiftance in this delicate branch of his bufinefs from foine 

 of his fpiders. This hint was not loft,* — and hence Bradley's 

 method of obferving feems to be carried to the higheft degree 

 of perfection by the affiftance of a harmlefs infect which is 

 perfecuted without mercy by every file de clutmbre throughout 

 his Majefty's dominions. 



There is, however, another method of obferving which Another method 

 precludes the neceffity of very fine wires. This confifts in jj d ° o f "jJJ" ^j— 

 noting the time when the centre of the ftar comes to the side 

 of the wire. But before this method is ufed it is neceflary that 

 one fide of the middle wire fhould be brought into the meri- 

 dian; fuppofe it be that fide which appears to the weft when 

 the telefcope is turned to the fouth, then the obfervations are 

 to be taken on that fide of all the wires. 



It is a line drawn by tkejlrength of imagination down the mid- Which is a real 

 die of the wire, parallel to the fides, which is ufed in Bradley's 

 method, but in my method a real line is prefented to the eye 

 of the obferver and which he fees very diftincUy, although as 

 fine as if it had been drawn through a geometrical definition. 



This method of obferving feems to be more fimple than the * ts advantages, 

 other, in confequence of its being, in many cafes only necef- 

 fary to attend to one fide of the wire : for example : Should 

 the clock beat when half the ftar is covered by the wire, it is 

 evident that the centre of the ftar pafTes the fide of the wire at 

 that time. And by making ufe of the apparent diameter of 

 the ftar, and the thicknefs of the wire as two meafures, the 

 fractional part of a fecond may be eftimated, by an experienced 

 obferver to a very great degree of precifion. 



How far this fmall alteration in the method of ufing the 

 tranfit telefcope may be found convenient to others experience 

 mull determine; but for my own part, I am certain that I can 

 obferve, not only with more eafe to myfelf, but with greater 

 exaclnefs by this method than by Bradley's. 

 I am, Sir, 



Your very humble fervant, 

 Lj/m, April 19, 1802.. EZEKIEL WALKER. 



# See a further account of this invention in the laft vol. of this 

 Journal, pa. 319, 



VI. Defer iption 



