llV INTRODUCTION TO THE 



The whole instrument was constructed in the most substantial yet highly finished manner by- 

 Messrs. Pistor & Martins, at Berlin, and is mounted on massive piers of red porphyry, based 

 on the native rock. 



Usually, all the adjustments were carefully examined both before and after each series of 

 observations. That for horizontality of the axis, by not less than six readings in reversed 

 positions of the level ; the nadir point, by reflection of the stationary horizontal wire from a 

 basin of mercury ; the line of collimation, from the ascertained level error and distance between 

 the central vertical wire and its image, as seen from the surface of mercury, and measured with 

 a micrometer screw ; and the azimuth, from the transits of fundamental stars of the Nautical 

 Almanac. The same pairs of stars in each series were observed quite uniformly through the 

 pre-appointed period. 



Explanation of the printed observations. 



Column 1 contains the number and letter for reference to the foot notes. 



Column 2 contains the year and day. 



Column 3 contains the name of the object observed. The names of the catalogues from which 

 the stars in this column have been selected are already given. 



Column 4 contains the means of the transits over the several vertical wires The reduction 

 of broken observations to mean of wires has been performed by means of the equatorial 

 intervals adopted for the specific period given in the introduction to Volume IV. 



Column 5 contains the instrumental corrections. These are the algebraic sums of the several 

 corrections for collimation, level, and azimuth, which will be found under the corresponding 

 date in Volume IV. 



Column 6 contains the clock error, derived from fundamental stars of the Nautical Almanac, 

 brought forward to the date of observation by rates deduced from errors on the previous and 

 subsequent nights. 



Column 7 contains the apparent right ascension of the limb of the planet and star as observed 

 at transit over the meridian of Santiago. The azimuth error has been deduced from the appa 

 rent places of the observed stars given in the Nautical Almanac. But as the limited comparison 

 which it has been possible to institute conclusively satisfies me that many, if not all, of the 

 southern circumpolar star places must be corrected before the true instrumental errors will be 

 positively known, the right ascensions now given will, therefore, most probably differ from 

 those of the same objects that will be found in Volume IV. 



Column 8 contains the mean of the four readings of the circle microscopes. When the object 

 was observed with a micrometer wire, the fact is stated in a foot note, and its distance from the 

 stationary wire or parallel of reference is given in revolutions of the micrometer head. In all 

 such cases the equivalent arc interval has been applied with the proper sign. 



Column 9 contains the refraction. This has been computed from the constants given in 

 tables published as an appendix to the volume of Washington observations before mentioned. 



Column 10 contains the nadir correction adopted for the special series from determinations 

 immediately preceding or following the observations. 



Column 11 contains the semi-diameter of the planet as given in the Nautical Almanac. 



Column 12 contains the observed apparent declination of the centre of the object at transit 

 over the meridian of Santiago. In the Mars series, when the difference of right ascension 

 between the planet and comparing star was too small to permit the circle micrometers to be 

 read in the interval of their transits, then the circle was clamped before the preceding object 

 came into the field, and the slow motion screw was turned until the stationary horizontal wire 

 accurately bisected the star, or was tangent to the planet s limb at the middle vertical wire, if 

 the latter preceded. When the second of the two objects entered, the micrometer screw carrying 

 the horizontal system was turned until the nearest wire bisected or was tangent to its limb in 



