﻿180 Shepard's Treatise on Mineralogy. 



posed to have, (a cube,) I grant that it would establish its spe- 

 cific character, but the "negative evidence" seems to be as much 

 against Chathamite as in its favor. 



Lincolnite. — In your measurement of Heulandite you suppose 

 M : e to correspond with the lateral angle of Lincolnite instead 

 of T : e, as shown by us in the last volume, p. 416. Taking 

 your new angles of Heulandite as correct, they give us 116° 17' 

 for the angle Tie, or the prism of Lincolnite. This angle is 

 1° 5' nearer your measurement of Lincolnite than that deduced 

 on the page referred to. 



Lederite.— In your original description of Lederite, (this Jour- 

 nal, Vol. xxxix, p. 359,) you state that the limits of variation in 

 the observed angles " were generally within 40'." We find on 

 comparing the angles with on| another, reasons however for as- 

 suming much larger limits ; for example, if the angles P : a and 

 M : a (see the volume just referred to) are correct, P : M is ne- 

 cessarily 2° too large, as results from the fact that the three an- 



M 



M 



2° out of the way. There is therefore some reason for the al- 

 lowances that are made in Vol. xlvi of this Journal. 



Mr. Dana has handed me some new measurements with the 

 reflective goniometer of the so-called Lederite, made on a small 

 and bright crystal, put into his hands by myself, (from Ham- 

 mond,) in order if possible to settle the claims of this mineral. 

 The crystal is nearly identical in form with that figured by your- 

 self, except that the smaller planes are too minute for measure- 

 He obtained, as he informs me, the following angles for 

 M : M, (r : r of the figure in Vol. xlvi, p. 3G,) which are the 

 results of the first five trials, and were obtained without previ- 

 ously acquainting himself with the particular angle of sphene, to 

 T,d^ he su PP° sed them to correspond. They are as follows: 



ment. 



stead 



finniu • - -'"cu UJf yuu. i^uw r: r is given Dyrnuupo 

 K mwbich it is called d' on d' ) at 1 13° 24', and by Mohs at 1 1 3° 27' ; 



a coincidence leaving little doubt of the identity with sphene. 

 seem! IlTj W Y ° Ur %"* is identical with Phillips' e», as 



mem of Ph'u ' ^ ^ e a:ais within & of the measure- 

 ment of Phillips. Yours, & c R S Jr 



Ya.e Co„e ge Labo^, *j£ ^ ^ R S ' * 



