Prof. Hansteen on Hourly Mean Temperatures. 309 



brown hematite are uniformly covered with a stratum of pyro- 

 lusite. ■ The same is found also in masses of larger dimensions 

 at Friedewalde in the county of Sayn, and in these the con- 

 centric disposition of the brown and black layers of the two 

 species, visible in the cross fracture, gives the whole a particu- 

 larly elegant appearance. Pyrolusite occurs in England at 

 Upton Pine, near Exeter, in Devonshire, and in Cornwall. 



The manganese oxide* noir barytif'ere of Haiiy, from Ro- 

 maneche, near Macon, does not appear to be a simple homo- 

 geneous mineral. When examined with the magnifying lens, it 

 exhibits distinctly a compact and a fibrous substance mixed 

 up with each other. The latter, as far as the minuteness of the 

 particles will allow, shows the properties of pyrolusite, its colour 

 and general aspect, and its hardness ; for even on the fracture 

 newly obtained this compound soils the fingers, though on the 

 file the hardness appears as high as 5.0... 5.5, that is, superior 

 to apatite. The compact mass is aggregated into reniform 

 shapes, which leaves numerous interstices between them. The 

 colour is nearly the same as that of the uncleavable manganese- 

 ore, a bluish or grayish black passing into dark steel-gray. 

 The streak is black, with a slight tinge of brown ; the place 

 on the mineral where it has been examined becomes shin- 

 ing. 



N. B. — The analysis of pyrolusite, and of the mineral from 

 Romaneche, will be found in page 861 of this Number. 



Art. XIX. — Comparison of the Hourly Mean Temperature 

 at Christiania and Leith in February and July. By Pro- 

 fessor Hansteen. Communicated by the Author. 



1 he observations contained in the following table are given 

 in degrees of Fahrenheit's scale. Those for Christiania were 

 made in the year 182? ; and those at Leith are taken from 

 Dr Brewster's paper published in the Edinburgh Transac- 

 tions , vol. x. part ii. and are the means of four years observa- 

 tions made in 1822, 1823, 1824, and 1825. 



