Royal Astronomical Society. 71 



sions of the same stars was only completed, and the results given to 

 the Society, in the course of the last year. They have, however, 

 already been printed, and will appear in our forthcoming volume. 

 Although the number of stars contained in this Catalogue is not 

 large, it acquires importance and value both on account of the still 

 relatively defective state of our knowledge of the absolute positions 

 of the southern stars, and from the circumstance that it is the first 

 which has been deduced from observations made in the southern he- 

 misphere with instruments equal to those of the best European ob- 

 servatories. Indeed, if we except Mr. Johnson's excellent Catalogue 

 of Stars observed at St. Helena, it must be regarded as the first in 

 which the places of stars not visible in our latitudes have been de- 

 termined with the precision and certainty now aimed at in astro- 

 nomy. It was principally with a view to the determination of the 

 positions of the principal southern stars, for the aid of navigation, 

 that the establishment of the Cape Observatory had been urged 

 upon and undertaken by the government, and this catalogue forms 

 one of the most important instalments astronomy has yet received 

 from it. 



Although the determination of the absolute places of the stars 

 formed the principal business of the observatory, Mr. Henderson 

 was too zealous an astronomer to omit taking advantage of the cir- 

 cumstances in which he was placed to investigate various important 

 points which can only be determined by a comparison of observa- 

 tions made at places remote from each other, or which acquire a 

 special interest from the position of the observer. A point of this 

 latter kind is the amount of refi'action in the southern hemisphere. 

 In an interesting paper on this subject, printed in vol. x. of the 

 Memoirs, he has given the results of a series of observations made 

 at the Cape, of stars having a greater zenith distance than 85°, both 

 north and south, and compared the refractions thence deduced with 

 the tables cf Bessel and Ivory. As tending to throw light on the 

 important subject of horizontal refractions, these results are valuable 

 with reference to general i^hysics as well as to practical astronomy. 



Another important determination, also prompted by the locality, 

 was that of the moon's horizontal parallax. It is well known that 

 the determination of this element was one of the principal objects of 

 Lacaille's voyage to the Cape ; his purpose being to obtain observa- 

 tions of the moon's declination corresponding to others made at dif- 

 ferent European observatories. A similar investigation was proposed 

 for Mr. Henderson, or rather several stars had been marked in the 

 Berlin Ephemeris and Nautical Almanac as favourably situated for 

 having their declinations observed along with the moon's in both 

 hemispheres, by which means the moon's apparent declinations are 

 obtained free from the effects of errors in the assumed declinations 

 of the stars. But the number of corresponding observations of this 

 kind which could be made, being found to be too small to permit the 

 element to be determined from them with sufficient accuracy, Mr. 

 Henderson had recourse, whenever there was a deficiency of moon- 

 culminating stars, to such of the principal stars as were observed. 



