R. B. Riggs — New Meteoric Iron. 59 



Rowland instrument. However, compensating advantages are 

 not wanting. The Rowland apparatus integrates all impressions 

 received at the slit. The ordinary comparison prism cannot be 

 used with it, and the lower orders of spectra are too narrow to 

 admit of convenient division at the camera; in fact, the spectra 

 begin at nothing at the slit and spread in a widening band as 

 we move toward the higher orders. 



The new instrument possesses the advantages of the analyz- 

 ing spectroscope. The spectrum can be made wide or narrow, 

 or divided at the slit. A preliminary trial has given the fol- 

 lowing results: — A flat grating of 14,000 lines to the inch and 

 a ruled surface 2xl|- inches was employed with a lens of 37 

 feet focus. The latter was placed close to the grating, and its 

 spectrum observed near the slit. In the second spectrum b 1 

 and b 2 were fully an inch apart as projected on a screen, and D 1 

 and D 2 had a separation of 13 to 11 mm. 



The excellence of the definition is shown by the fact that 

 with an ordinary reading glass of six inch focus, E was seen 

 double, and 11 lines were counted between D 1 and D 2 . With 

 this form of apparatus the amount of dispersion can be varied at 

 pleasure by simply altering the relative distances of slit and 

 camera from the grating, but in such a way that slit and camera 

 shall occupy conjugate foci of the lens. 



Jefferson Physical Laboratory, Harvard University, June 3, 1887. 



Aet. IX. — A new. Meteoric Iron and an Iron of doubtful 

 nature ; by R. B. RlGGS. 



TJie Abert Iron. 



This meteorite was found entire and unlabeled in a collection 

 of minerals made by the late Col. J. J. Abert, and presented to 

 the National Museum by his son, Mr. J. T. Abert. It weighed 

 originally 456 grams. Its specific gravity was found to be 7"89. 

 Its cross section measured 50 mm by 37 mm . An analysis gave it 

 the following composition : 



Fe 92-04 Graphite -03 



Ni 7-00 C (combined) _ . '02 



Co -68 



P . -08 99-86 



S -01 



In composition, therefore, it. is similar to the Nelson County 

 meteorite. Nitric acid brought out characteristic Widman- 

 statten figures of the same octahedral marking with, though 

 somewhat coarser than, those of the Grand Rapids meteorite. 

 The fracture is distinctly octahedral. 



