IOU 



ASTRONOMY. 



[TRANSIT OUSERVATI. >.<. 



for the distance in are of each wire from the mean of 

 aU: 



For Wire I. + 10 '.'1 645 



II. + i. 



III.+ 327239 



IV. - 0-033 



V. - 327171 



VI. - 654-809 



VII. -1021509 



s. 



or + 41 n:i 

 + 27<.l.i 



- OO02 

 -13811 

 -27-654 

 -41-438 



Dr. Drew ha* usefully applied a wire micrometer, 

 attached to a five feet telescope, fur the determination of 

 the intervals of his transit circle an instrument of forty- 

 two inches focal distance. The value of one revolution 

 of the micrometer being known, he was able to measure 

 easily the distances of the wires, by directing the two 

 object glasses towards each other. The result agreed 

 closely with that deduced from a transit of 2 Ursio 

 Minoris. 



To find the correction to an imperfect transit of the 

 moon or a planet : 



Let h* be the apparent distance from the middle wire. 

 ,, ft = the right ascension of thu zenith. 

 a'= the apparent right ascension of the interval. 

 t'=* the apparent declination. 

 Then we have 



Sin. h cos. 6' sin. jt a' < ,, cos. sin. (/ a). 



Put sin. A A sin. ]', and sin. ft a ~/i-o sin. 1'. 

 Then we shall have 



. d cos. t 



A d , (p-a) . . . it -a 



d cos. S ' 



This is the expression for all those bodies which do not 

 change their right ascension. The fixed stars are tliu 

 mily unea which do not, and their distances are so im- 

 mense, that a' and d may be regarded as equal, which is 

 also the case with the planets, on account of their dis- 

 tance. Let X* be the moon's or planet's increase of 

 It. A. in one second of time, then (1 X)' is the equa- 

 torial space described by the moon or planet in one 

 second of sidereal time ; consequently, the sidereal time 

 of describing p a, will be represented by 





~ (1 + X) d cosTa 



Geo. Z. D. 



* 



This is the formula given in the Greenwich Obierva- 

 tiuns for the same purpose. In the case of the planets 

 d is very nearly equal to d, and the formula is 



(1 + X ) X 



cog 



where X is the increase of the planet's 



right ascension in one second of sidereal time. 



COMPLETION Or AN IMPEBFECT TRANSIT OF TUB MOOX. 



1848, August 9. 



o / 



D'sgeo. N.P.D 10741 



Co. lat of Greenwich 38 31 



5 's geo. Z. D , 



Parallax in altitude . 



J's app. Z.D. . 



tilt 5'J 



I = 131* -62 = the increase (in seconds of time) 

 of the Moon's right ascension for a transit over 

 a meridian upon the earth, distant by Ih. of 

 terrestrial longitude (Nautital Almanac, 1848, Sec- 

 tion Moon-Culminating Stars). 



0-01659 



Log. 3COO +! 

 3000 



Log. sin. J'sgeo. Z.D 9 !>7(H;t 



AT. co. log. sin. J'sapp. Z.D '02706 



Log. sec. J'sgeo. dec! 0-02102 



1848, August 9th. 

 Wires observed. 



For an 



tx 

 Star. 



. ( A . 



ial I'. . 

 ( . 



+ 38-511] 

 85-711 

 12-840 



+ 25-687* 



Log. 25-687 (see below*) 



Completion of imperfect transit, l<> reduce, to 

 mean of sovuii wired . . , 



j 



0-03431 



1-40972 

 1-44403 



2779 



