Dr.Wackenroder's Examination of the Diopside qfFassa. 349 



ment s ; at the equator, the compression e has greater influ- 

 ence on the length of a meridional arc, than at any other po- 

 sition on the surface of the globe ; and it follows that two arcs 

 of considerable extent, in the situations mentioned, combined 

 with other good measurements in our possession, must lead 

 to a very exact determination of the elliptical elements of the 

 figure of the earth. One remark it seems important to add; 

 namely, that the ellipticity cannot be determined with any 

 precision by combining different degrees of the meridian mea- 

 sured in England ; because the element sought has little in- 

 fluence on the lengths of such degrees. And this observation 

 may be extended to all latitudes within 15° or 20° of 54° 44' 

 on either side; within which limits the ellipticity contributes 

 only an inconsiderable share to the length of a meridional arc. 

 And what has now been said will serve to explain the discre- 

 pancy of the ellipticities deduced by combining different de- 

 grees of the meridian within the boundaries of England and 

 France ; and likewise the great variation between the quantities 

 so obtained, and what is found by the comparison of remote 

 degrees. These observations may be illustrated by examining 

 the equations (B). In the English and Swedish measurements, 

 the coefficients of i are small, and have opposite signs. The 

 coefficients of the same quantity are nearly equal in the French 

 and Peruvian arcs, although the former has more than four 

 times the length of the latter. In the Indian and French 

 measurements, the coefficients are as 3 to 1, while the arcs 

 themselves are as 3 to 4 ; and this shows how important it is, 

 for the exact determination of the ellipticity, to have a large 

 arc near the equator. 



April 12, 1828. J. Ivory. 



LV. Mineralogical and Chemical Examination of the Diopside 

 of Fassa in the Tyrol, By Dr. H. Wackenroder, Pro- 

 fessor of Chemistry at Gottingen*. 



A MONG the various new minerals discovered by Bonvoi- 

 •f~ sin-j- during a journey through Piedmont, there were two 

 which this mineralogist considered as distinct species of mi- 

 nerals ; and he called them, after the places in which they were 

 found, Mussite and Alalite. According to an account given 

 by Tonnellier %, Haiiy found in the crystalline form of these 

 two minerals such a degree of conformity as induced him to 



* Communicated by the Author. 



t Journ. de Vhys. par Delametherie, torn. Ixii. p. 418, 423. 



% Journ, des Mines, torn. xx. p. 65. 



consider 



