580 Royal Astronomical Society. 



means confined to the northern regions of the sky, though origina- 

 ting about the magnetic north ; that, with the exception of a dimi- 

 nution of its general effect, it is uninfluenced by moonlight ; that its 

 appearance generally accompanies weather the reverse of frost, such 

 as heavy wind and rain ; and, lastly, that it is wholly inaudible. The 

 author concludes by warning the spectators of this phenomenon 

 against the false impressions to which the senses are liable, especially 

 with regard to the sensation of heat and the notion of sound, as at- 

 tending phenomena in which our idea of either of these qualities 

 has been predominantly awakened. 



Mean Positions of the Stars mentioned in Mr. Baily's Address 

 to Observers, determined at San Fernando in the years 1834, 1835, 

 1836, 1837, and 1838. By M. Montojo. Translated by Captain 

 Shirreff, R.N. 



The whole number of stars contained in this catalogue is 126, of 

 which 121 are mentioned in Mr. Baily's " Address to Observers," 

 as being of doubtful position, or not recently determined. The re- 

 ductions of the observations of right ascension have been performed 

 strictly by means of the Tabulce Regiomontana, the mean positions 

 of the fundamental stars and the numbers and constants of that 

 work having been adopted. The equinox to which they are referred 

 is that of Bessel, coinciding with that determined at San Fernando 

 from 206 observations of the sun. 



The transit-instrument and clock employed are described in the 

 published Observations of the years 1834 and 1835 ; and the instru- 

 mental errors there explained have been rigorously taken into account. 



The observations in declination include only the years 1837 and 

 1838, the mural circle having come into operation in 1837. 



This instrument differs in no essential respect from those of the 

 Observatory of Greenwich, and was made by Mr. T. Jones. 



The mode of observation is essentially similar to that pursued 

 with other mural circles, the horizontal points being obtained by 

 direct and reflexion observations, at the same transit, of different 

 stars ranging through a large arc of zenith distance, and the mean 

 of the results of three days' observations being usually employed. 

 Each observer is made to determine his own horizontal point, some 

 slight disagreement between the results of different observers, si- 

 milar to what in transit observing is called personal equation, having 

 been recognised. 



The latitude was determined by superior and inferior transits of 

 Polaris, of /3, 8, and A Ursse Minoris, and of Cephei 51 (Hev.), using 

 only such observations of them as were made by direct vision and 

 by reflexion at the same transit. 



The refraction is computed from the Tabulce Regiomontanee, and 

 the precession from the values of m and n given in that work. 



The resulting right ascensions are compared with the Astrono- 

 mical Society's Catalogue, with Pond's Catalogue of 1112 Stars, 

 with Wrottesley's Catalogue, and with Johnson's of 606 Southern 

 Stars, and also with the stars found in the Greenwich observations 

 of 1833, 1836, and 1837. 



