410 



Observations of the Transit of Mercury. 



[Sept. 



clean circular spot, surrounded with a slightly enlightened ring ; his 

 diameter was as near as could be estimated, that of one of the micro- 

 meter wir es. 



The time occupied by the passage of the sun's disc across the wires 

 decreased as the evening advanced, from the effect of the atmospheric 

 refraction contracting his vertical diameter. 



Transits of Mercury and of the limbs of the Sun, past the wires of an equatorial tele- 

 scope in mean Solar Time, at Calcutta, Lat. 22° 36' 21'' Long. 5h. b3m. 28s. 





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H. M. S. 



M. 



s. 



M. S. 



M. S. 



M. s. 





1 



4 30 44.3 







31 59.5 



32 57.6 



2 13.3 



58.1 



2 



33 54.4 



34 



10.3 



35 09.0 



36 07.8 



2 13.4 



2 58.8 



3 { 



46 40.8 



46 



57.2 



47 51. : j , 



48 54.2 



2 13.4 



1 02.9 



47 04. S 



47 



21 6 



48 17.0 



49 186 



2 137 



1 01.6 



4 



49 40.6 



49 



56.4 



50 50.4 



51 52.6 



2 12.0 



1 02.2 



50 05.3 



50 



20. f. 



51 15.2 



52 17.6 



2 12.3 



1 02.4 



H 



52 36.5 



52 



52.5 



53 45.5 



54 48.3 



2 11.8 



1 02.8 



53 01.5 



53 



16.7 



54 09. 9 



55 13.7 



2 12.2 



1 03.8 



*{ 



5 00 06.3 



00 



23.0 



01 145 



02 17.5 



2 11.2 



1 03.0 



00 33.7 



00 



49. 3 



01 40.5 



02 45.6 



2 11.9 



1 05.1 



? { 



03 38.0 



03 



54.3 



04 44.7 



05 50.3 



2 12-3 



1 05.6 



04 04.3 



04 



19 7 



05 lO.k 



06 15.7 



2 11.4 



1 05.5 



*{ 



16 05.6 







17 09.1 



18 17.8 



2 12.2 



1 06 .7 



16 33.8 



16 



59.4 



17 36 6 



18 45.8 



2 12.0 



1 09.2 



Means 



4 54 37.7 







4 55 46i. 



4 56 50.0 



2 12 4 



1 03.4 



Time o 



f O's passin 



y meridian b 



y Nautical / 



ilmanack,. . 



2 12.28 





Distance from Mercury's centre to the tangent of the northern 

 limb of the sun, measured with a wire micrometer. 



At 



Mean Solar 

 Times. 



h. m. s. 



4 40 00 



4 57 14 



5 07 24 



Divisions 

 of the Micrometer. 



509 

 530 



568 



In space. 



5 55.4 



6 10.1 

 6 36.6 



The sun's horizontal diameter measured by the same micrometer, on 

 the 7th May, 6 p. m. was 2727 divisions. By the Nautical Almanack 

 for the same period, it was 1904.0 seconds, which makes the value of 

 the divisions 1.4S2 per second. 



There is too much discrepancy among the foregoing measure- 

 ments to allow of their being individually useful ; the utmost that 

 can be expected from them is the determination of the position of 

 Mercury on the sun's disc at one mean period. As I hope this will be 



