126 



iron, mixed with a portion of argill. Its appearance altogether might 

 easily induce mineralogists to refer it to that kind which has been 

 distinguished by the name of Arragonite ; but various reasons are 

 here assigned for considering them as distinct substances. Chemical 

 analysis has not yet afforded any criteria for distinguishing this spe- 

 cies either from the arragonite or the common carbonates of lime. 

 And it is lastly thrown out, merely as a conjecture, whether its 

 greater degree of hardness and specific gravity may not be owing 

 merely to its constituent particles being more minute and more closely 

 connected. 



The second part of this paper, which treats of a new species of 

 oxide of iron, is prefaced by a short survey of the different appear- 

 ances of the oxides of iron, according to their various degrees of 

 combination with oxygen : and it is here suggested, that not only 

 the proportion of oxygen, but also the mode of combination, may 

 contribute to produce varieties which cannot by any other means be 

 accounted for. The new species here described is thought to hold 

 its place between the slightly attractable oxide of iron called Specular 

 ore, or, by Abbe Hauy, fer oligiste, and that kind which no longer 

 crystallizes except in a very indeterminate form. Its surface is of a 

 gray colour, and has a specular appearance : it is not at all acted 

 upon by the magnet, and seems to be the last degree of oxidation 

 in which iron retains the property of crystallizing in a regular form. 

 This form is a perfect cube ; its fracture is conchoidal ; its hardness 

 is rather inferior to that of the slightly attractable oxide of iron ; its 

 specific gravity only 3961. 



To this species it seems ought to be referred the Eisen-glimmer of 

 the Germans, when it is not attractable. When at all acted upon 

 by the magnet, it ought to be numbered among the slightly attract- 

 able oxides of iron. Specimens of this new species have been brought 

 from Lapland, and are often found mixed or embodied in other oxides 

 of the same metal. 



The author, lastly, points out how, by the red colour of the pow- 

 der and by scratching, this species may be, in a general way, distin- 

 guished from the others ; an object of no trivial importance, since 

 the products of metal from the ores may be influenced by this discri- 

 mination. 



Account of the Changes that have happened, during the last Twenty -five 

 Years, in the relative Situation of Double-stars ; with an Investiga- 

 tion of the Cause to which they are owing. By William Herschel, 

 LL.D. F.R.S. Read June 9, 1803. [Phil. Trans. 1803, p. 339.] 



After some general observations on the various discoveries lately 

 made, which have contributed to extend our knowledge of the con- 

 struction of the heavens, Dr. Herschel assumes as a possibility, that 

 among the multitude of the stars in the firmament, there may be in- 

 stances of pairs of stars of the same or different relative magnitudes, 

 which may revolve, either in circles or ellipses, round their common 



