On the Latitude, >$-c. of the Observatory/ on the Cult on Hill. 257 



which the ores experienced by exposure to a red heat, and 

 that I was ignorant of the well-known fact, that some of these 

 oxides lose oxygen as well as water at that temperature. You 

 must have overlooked a portion of my Essay altogether, other- 

 wise you would not have made the supposition. By referring 

 to the commencement of the second part of that Essay, you 

 will find that the water was in every instance ascertained by 

 heating a known quantity of the ore to redness, and collecting 

 the aqueous vapour in a tube filled with fragments of the 

 chloride of calcium. This method is at least as accurate as that 

 adopted by yourself, and gives results of great uniformity. 

 The specimen of Ihlefeld manganite which accompanies this 

 letter, will enable you to correct me if I am in error. Of 

 course the same doubt, as applied to the analysis of psilome- 

 lane and the manganese oxide baritifere, is equally inappro- 

 priate. The difficulty of discovering the atomic nature of these 

 compounds arises, as I have mentioned in my Essay, from 

 their impurity. The latter is visibly interspersed with parti- 

 cles of the peroxide; and the former, from its analogy to the 

 other, and from the intimate manner in which it is associated 

 in nature with the peroxide, is, I believe, equally impure. 



Some of your remarks on the formation of what is called 

 the red sulphate of manganese, appear to me perfectly correct : 

 I shall waive, however, any further comment on this compound 

 at present, and will probably make it the subject of a future 

 communication. 



I remain, my dear Sir, very truly yours, 



University of London, March 5, 1829. Edward TurNER. 



XL. Determination of the Latitude and Longitude of the 

 Observatory on the Calton Hill. By William Galbraith, 

 Esq. A.M. 



To the Editors of the Philosophical Magazine and An7ials. 



Gentlemen, 



Edinburgh, July 14, 1827. 

 TT appears to me that the problem originally proposed by 

 ■• Richard Townley, Esq. and resolved by Mr. John Collins, 

 in the Philosophical jTransactions, No. 69, and has since been 

 repeatedly given in various publications, might be advantage- 

 ously extended to more generally usefid purposes than it has 

 been hitherto. 



As I had occasion to give a small table of the latitudes and 

 longitudes of places, I was desirous of inserting that of the 



N. S. Vol. ."5. No. 28. April 1829. 2 L new 



