Dr. Walchner's Examination of Hyalosidcrite. 181 



length may consult the Monatliche Correspondenz by Baron 

 Zach, vol. xvii. xxiv. and xxvi. ; where he will find formulae 

 adapted, by M. Bessel, to almost every case that can arise in 

 practice. See also Santini's Element i di Astronomia, vol. i. 

 page 261. 



Although I have, in this communication, alluded only to 

 the immersion and emersion of the bodies with respect to the 

 inner circumference of the ring, yet it is evident that the same 

 principles may be applied to the immersion and emersion of 

 the bodies with respect to the outer circumference of the ring, 

 at «■, <r, and w', <r', respectively. And these double observa- 

 tions will tend to ensure greater accuracy. M. Frauenhofer 

 however considers that the edge of the inner circle is more 

 perfect than that of the outer one. 



It must be evident that the correctness of any results, de- 

 duced from a micrometer of this kind, will depend on the ac- 

 curacy with which the circles are turned and finished. In 

 this respect M. Frauenhofer's micrometer seems as perfect as 

 human skill can make it : and it certainly does credit to the 

 talents of this distinguished artist. 



XXXII. Miner alogical and Chemical Examination of Hya- 

 losiderite, a new Mineral. By Dr. Walchnek, of 'Freiburg 

 in the Breisgau.* (With a Plate of Crystals.) 



I. Mincralogical Description. 



§ 1. 

 r | "'HE mineral, of which I now communicate an examina- 

 ■*■ tion, is found on the Kaiserstuhl in the Breisgau, a 

 rock belonging to the trap formation, in the neighbourhood 

 of the village Sasbach, in a basaltic amygdaloid, of a reddish 

 and liver-brown colour, accompanied with augite and bitter 

 spar. 



I found it so long ago as the year 1819, when on a minera- 

 logical excursion which I undertook upon this interesting 

 mountain. The opinions concerning it were very various : 

 sometimes it was declared to be olivine, and sometimes it was 

 pronounced to be augite. Both assertions appeared to me im- 

 probable, and I felt inclined to look npon it as a mineral 

 hitherto unknown. A more particular examination of its 

 form and composition strengthened my opinion. At Gottin- 

 gen, where I afterwards continued my studies, I resumed 

 my investigation of the subject, and communicated the re- 



* From Schwcigger's Neva Journal fiir Chemie,&C, band ix. p. 65. 



suits 



