144 Lord Oxmantown on Reflecting Telescopes. 



becomes warm, and the polisher is almost dry ; and I rather 

 think that practical opticians suppose it is impossible to com- 

 municate a fine polish without this mode of proceeding. From 

 the experiments which I have tried, I have little doubt but 

 that the figure of the speculum is injured by working it upon 

 a polisher nearly dry, and that the injury is in some degree pro- 

 portional to the time it is so worked : — at any rate large metals 

 must be finished upon a moist polisher. Until very lately I 

 had not found out a method of communicating a very fine 

 polish to a cold metal worked upon a moist polisher. 



As fine a polish as can be desired can now be given to a 

 metal of any temperature which we may fix upon above the 

 freezing point. Both theory and practice lead to the same 

 conclusion, that it is desirable to polish a speculum at a tem- 

 perature as nearly as possible the same as that at which it is 

 to be afterwards used, particularly if the speculum is of large 

 dimensions. 



In the preceding account, I have endeavoured to give a ge- 

 neral outline of the different objects which I have attempted 

 to effect, and I have, as far as was in my power, conveyed an 

 accurate idea of the degree in which I conceive I have been 

 successful. Further experiments shall be tried, and the spe- 

 cula already completed shall be subjected to the severest tests. 

 Should I then feel satisfied that specula obtained by these pro- 

 cesses are as perfect as I have ventured to anticipate, I shall 

 then have the pleasure of placing some of them in the hands 

 of the able and persevering observers of the present day, where 

 they will be fairly tried, and, if they have merit, will certainly 

 not remain idle. 



The examination of the heavens commenced by the late Sir 

 William Herschel, and, prosecuted by him with such success, 

 still continues. New facts are recorded ; and there can be 

 little doubt but that discoveries will multiply in proportion as 

 the telescope may be improved. 



It is perhaps not too much to expect, that the time is not 

 far distant when data will be collected sufficient to afford us 

 some insight into the construction of the material universe. 



