158 Re-examination of Microlite and Pyrochlore. 



may I think, be deemed a close approximation to the truth. On 

 comparing the result last obtained with those of former observa- 

 tions, it is evident, that the westerly variation, which has been 

 for years increasing, is still advancing, though at a diminished 

 rate. 



The inclination, or magnetic dip, was obtained by numerous 

 observations between the 20th of September and the 10th of No- 

 vember of the same year. Those of the latter month were made 

 at various localities within the compass of a mile, a condition 

 which proved of importance. The instrument employed was 

 one made by Gambey, furnished with two needles, manifestly a 

 good article. An equal number of observations was made before 

 and after the noon of each day; an equal number in each period 

 with each needle ; an equal number of the observations was taken 

 with the instrument facing east and west, and an equal number 

 with the poles of the needles reversed. The readings consisted 

 of the mean of both ends of the needles, and the result of all, in- 

 dicated a dip of 73° 4K25. 



How far the means employed in obtaining these elements, will 

 entitle these results to confidence, is for those interested in the 

 subject to judge ; in the practical details, neither care nor labor 

 has been spared. 



JVan tucket, Nov. 11, 1843. 



Art. XIX. — Re-examination of Microlite and Pyrochlore ; by 

 Augustus A. Hayes. 



The July number, for 1842, (Vol. xliii, p. 33,) of this Journal, 

 contains a short paper, by Mr. J. E. Teschemacher and myself, on 

 the identity of microlite and pyrochlore. In the same number, 

 (p. 116,) Prof. Shepard has published an article entitled, " Want of 

 identity between Microlite and Pyrochlore." Mr. Teschemacher, 

 from studying the crystals of these minerals, arrived at the conclu- 

 sion that they are of the same species. Prof. Shepard has, in detail, 

 given his objections to the conclusions of Mr. T. As Mr. T. has 

 seen nothing in the reply of Prof. S. leading him to doubt the cor- 

 rectness of his statements, he declined noticing the article. It is not 

 my intention to offer any remarks on that part of Prof. Shepard's 

 paper which contains his objections on " natural history grounds." 



