228 Astronomical Society. 



powerful telescopes will probably be employed to show all the satel- 

 lites of the planet. I believe that large reflecting telescopes will 

 begin to supersede achromatic ones ; at least, I have no doubt they 

 are capable of greater perfection. They can be made M'ith mathe- 

 matical precision, which is not the case with achromatic telescopes. 

 I think, also, that opticians would have devoted their attention to 

 them in preference, if they had not been discouraged by their more 

 rapid destructibiUty. If the method of making an indestructible 

 metallic surface could be discovered, I should no longer doubt of a 

 still further perfection of the reflecting telescope. Could not hard 

 steel be made available ? and would it not, if proper care was taken 

 of it, be less destructible than the common metallic reflector ? 



II. Errors of Heliocentric Longitude and Ecliptic Polar Distance 

 of the planet Venus, computed from the Tabular Errors of R. A. and 

 N. P. D., given in the Cambridge Observations of 1836. By the 

 Rev. R. Main. 



Having been engaged in correcting the Elements of the Orbit of 

 Venus, it occurred to Mr. Main that the reduction of the Tabular 

 Errors of R. A. and N. P. D., derived from the Cambridge Observa- 

 tions of 1836, to errors of Heliocentric Longitudes and Ec. P. D., 

 would form a desirable supplement to his papers. 



He has added the equations which arise for the corrections of the 

 Node and Inclination of the Orbit ; and it is his intention to form 

 those for the corrections of the four remaining elements. 



He has used Mr. Airy's formulae contained in the tenth volume of 

 the Society's Memoirs, and divided the observations into gi-oups of 

 about the same length ; applying the same corrections to the Riglit 

 Ascensions for the Error of the Equinoctial Point. 



The general agreement between the errors, and those given in the 

 Greenwich Observations for 1836, shows the goodness of the obser- 

 vations, and gives additional confidence in the results to be derived 

 from them. 



The errors of the tables are then given, and equations for correct- 

 ing the elements. 



III. A Catalogue of 726 Stars, reduced to the year 1830, and de- 

 duced from the Observations made at Cambridge in the years 1828- 

 1835. By G. B. Airy, Esq., Astronomer Royal. 



The state of reduction in which the places of the stars had been 

 published in each of the annual volumes of the Cambridge Observa- 

 tions, left little to be done for the formation of this catalogue, ex- 

 cept the combination of the results of the different years. This was 

 done by applying to the mean of each year's results the annual va- 

 riation in the catalogue of this Society (except for stars near the 

 pole), so as to bring the places up to Jan. 1, 1830 ; and then taking 

 the mean of the diff^erent results for 1830, giving to each year a 

 weight proportioned to tlie number of observations. Special me- 

 thods of reducing some of the observations are fully explained in the 

 preface, to which it is not requisite here to aUude further; and a list 

 of the principal discordances are subjoined, as well as of some of the 

 observations that have been omitted in the reductions. 



