OF ARTS AND SCIENCES. 227 



the basic cbromate of chromium ; this proceeds on the assumption that 

 there is some other salt better entitled to the name of normal or neutral 

 chromate, as, for example, the imaginary chromate containing three 

 equivalents of chromic acid. Until some such chromate is discovered, 

 the word basic would be better omitted from the name of the only defi- 

 nitely determined chromate of chromium. 



Professor G. P. Bond exhibited a drawing of the great 

 nebula surrounding the star 6 Orionis representing its ap- 

 pearance in the twenty-three-foot refractor of the Observatory 

 of Harvard College. 



The feature to which attention was particularly directed was the 

 spiral structure of the principal masses of light, or, more correctly, the 

 tendency to an arrangement in elongated wisps or whirls, sweeping out- 

 ward from the bright region of the Trapezium. A disposition of the 

 nebulosity in some localities to radiate from the vicinity of the Trapezium, 

 noticed in the memoir published by Professor W. C. Bond in 1848, 

 has repeatedly attracted attention in subsequent years. The idea of a 

 spiral character in the i-adiations had even been suggested, without how- 

 ever presenting itself definitely to the mind as the true conception of 

 the leading features of the nebula. 



During the past winter, opportunities were taken to review the whole 

 region, with particular reference to this peculiarity ; attention being 

 given exclusively to the arrangement of the diverging wisjis of nebulos- 

 ity, and the alternating dark spaces by which they are separated from 

 each other. A particular scrutiny of the latter was of considerable 

 assistance in tracing the fainter convolutions. The form and disposition 

 of the whirls were thus defined by two independent processes, the neb- 

 ula being first sketched as a bright object on a dark ground, and, again, 

 its darker openings and channels as dark objects on a white ground. 



The quarter designated in Herschel's chart * as the Regio Godiniana 

 was first explored. The nebulosity was here resolved into an assem- 

 blage of three or four long wisps, interlaced with each other, or crossed 

 by offsets ; these were ultimately traced from a point near the northern 

 margin of the Sinus Magnus, over the whole length of the Regio Picar- 

 diana and the Regio Godiniana, forming a sweep of 1 20°, After pass- 

 ing the well-defined northern boundary of the last-named region, and 



* Mem. Astr. Soc, Vol. II. 



