lii 



INTRODUCTION TO THE 



continuedly until the work for the night terminated. Except in cases where the two objects 

 were so near in right ascension, or the space through which it was necessary to turn the 

 screw was so great that one reading was, of necessity, after the second object had passed that 

 wire, the difference of declination was measured by two independent readings of the micro- 

 meter when bisecting the star or tangent to the limb of the planet at transit over the middle 

 wire. The observation was always perfected by turning the micrometer in the order of the 

 number on its divided head and which was against the spring within the box. On one or, 

 perhaps, two occasions this space was so great and the difference of right ascension so little, that 

 it was indispensable to use both the slow motion screw of the declination circle and the 

 micrometer. As would be inferred, these observations are not at all satisfactory. 



To eliminate errors of irradiation and assumed semi-diameters, on all possible occasions the 

 consecutive observations were of opposite limbs of the planet. 



EXPLANATION OF THE PRINTED OBSERVATIONS. 

 Observations with the equatorial. 



The printed observations, pages 2 305, require very little explanation. 



The first column of each page contains the numbers for reference,. with occasional italic 

 letters, a, b, c, &c., indicating a note in the remarks accompanying each night's observations. 



The second column contains the name of the planet, and the catalogue from which the com- 

 paring star has been selected. N.P ; N.F ; S.P ; S.F, designate the limbs of the former ; 

 Rumker, 16V3, refers to his " Mittlere Oerter von 12.000 Fix-Sternen ;" Bessel, 405, refers to 

 the 405th zone of Bessel ; H.O. to the " Histoire Celeste" of Lalande ; and W. C., to unpub- 

 lished observations of the Washington Catalogue. 



The five following columns contain the seconds of observation over the five wires of the equa- 

 torial, and the eighth column, the mean of these times. Broken observations have been reduced 

 by means of the following equatorial intervals multiplied by the Secant of the declination of the 

 object. The intervals were deduced from 100 transits of comparison stars. 



Equatorial intervals. 



Column 9 contains the distance of the limb of the planet or star from the stationary horizontal 

 wire expressed in revolutions of the micrometer head. In both series of observations on Mars, 

 and in the first Venus series + signifies that the moveable wire is to the north of the stationary 

 wire, and vice versa. Prior to the second Venus series the micrometer was turned 180 so that 

 throughout these observations the symbols have the opposite signification. 



Column 10 contains the difference of right ascension between the planet's observed limb and the 

 star, at transit of the former over the imaginary centra] wire of the system 



Column 11 contains their difference of declination expressed in revolutions of the micrometer 

 -f signifying that the planet is to the north of the star, and vice versa. 



Columns 12, 13, and 14 contain the barometer and thermometer readings usually noted at 

 the commencement and close of the observations. 



Remarks respecting the condition of the atmosphere or other influence likely to affect the 



