1865.] President's Address. 511 



them, the President and Council have to recommend as follows regarding 

 the construction of the instrument contemplated. 



" () That the telescope he a reflector, with an aperture of not less than 

 four feet. This is essential, as no refractor would have the power required. 

 " (b) That the large mirror be of speculum-metal. Such mirrors can be 

 constructed with certainty of success, and at a cost which can be foretold ; 

 whereas the recently introduced plan of glass silvered by a chemical process 

 has not yet been sufficiently tried on so large a scale as that contemplated. 

 " (c) That the tube be constructed of open work, and of metal. Lord 

 Rosse has recently changed the tube of his three-foot altazimuth from a 

 close to an open or skeleton one, and it is understood that he intends doing 

 the same with his great telescope. Mr. Lassell's tube is also an open one, 

 which his experience leads him decidedly to prefer. 



*' (d) The telescope should be furnished with a clock-movement in right 

 ascension. 



" (e) Apparatus for repolishing the speculum should be provided. 

 " (/) With respect to the form of reflector to be adopted, some differ- 

 ence of opinion exists, as the Newtonian and Cassegrainian have each some 

 advantages not possessed by the other. On this point further corre- 

 spondence appears desirable ; but as the main features of the scheme are 

 the same in both cases, there does not appear to be any occasion to wait 

 till this point shall have been finally decided. 



" 5. With respect to the cost, something must depend on the solidity of 

 the construction and the perfection of the workmanship ; but if it be 

 assumed that the workmanship shall be of the best description, and the 

 instrument furnished, as seems desirable, with polishing apparatus, and a 

 second speculum for using while the other is being polished, it is probable 

 that the cost will not fall much short of ^OOO. 



" 6. It is estimated that the construction of the instrument will occupy 

 about eighteen months. 



" 7. It seems highly desirable that the future Observer should come to 

 England during a part at least of the time occupied in the construction of 

 the instrument, in order that he may become thoroughly acquainted with 

 all its details, and especially with the mode of repolishing ; and also that 

 he may personally acquaint himself with the working arrangements followed 

 at the Observatories of the Earl of Rosse and Mr. Lassell, who have 

 expressed thjeir willingness to afford him every facility." 



This Report, accompanied by several copies of the Correspondence ad- 

 verted to, was transmitted in due course to Melbourne. 



In 1863 Mr. Lassell made the most liberal offer of freely presenting for 

 the observations at Melbourne his own 4-foot reflector, with which he had 

 been carrying on a series of observations at Malta, as soon as that series 

 should be completed, or in the coarse of a year or two. The construction 

 of this telescope had been largely considered and discussed in the corre- 

 spondence already adverted to. On Mr. Lassell's munificent offer being 



