32 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



pate in proportion as it was propagated from the east to the 

 west. Donati on the Aurora of February 4, 1872. 



THE POLARIZATION OF THE ZODIACAL LIGHT. 



The difficulty of obtaining satisfactory observations in the 

 delicate question of the polarization of zodiacal light has been 

 at length successfully overcome by Professor Wright, of Yale 

 College. He states that numerous attempts had been made 

 by him to detect appearances of polarization with the ordi- 

 nary Savart polariscope, but never with any result except on 

 one favorable occasion, when, by the utmost exertion of visual 

 effort, the bands indicating the presence of polarized light 

 seemed to be visible by glimpses. The observation was so 

 uncertain, however, that it was considered worthless. Suc- 

 cess in this matter crowned Professor Wright's labors only 

 after he had, perhaps accidentally, found among the appa- 

 ratus belonging to the physical cabinet of Yale College a 

 quartz plate, which was cut perpendicularly to the axis, 

 and exhibited by polarized light an unusual intensity of 

 color. This plate consisted, essentially, of left-handed quartz, 

 through which passed, somewhat eccentrically, a narrow 

 band of right-handed quartz. This band was not bounded 

 by sharp lines of division, but by intermediate and still nar- 

 rower strips, which were of different structure, and appar- 

 ently formed by the interleaving of the strata of the two 

 portions at their edges. In the polarizing apparatus these 

 strips simply vary from bright to dark, without marked 

 appearance of color. Examined with one Nichols prism 

 and unpolarized light, the plate appears perfectly colorless, 

 and shows no trace of its heterogeneous nature. In order to 

 adapt this quartz plate to the observation of the zodiacal 

 light, it was placed in one end of a tube about eleven inches 

 long, at the other end of which was placed a Nichols prism, 

 the latter being easily turned upon its axis. Thus mounted, 

 it formed a polariscope of extraordinary sensibility, far excel- 

 ling the best Savart, when faint lines were to be examined. 

 The narrow strips are peculiarly advantageous, as, with a very 

 feeble illumination, they appear bright upon a dark ground, 

 or the reverse, and are thus easily seen. As a test of its deli- 

 cacy, it is mentioned that when a glass plate is laid upon the 

 window-sill, and the diffused lio-ht of the skv in a clear moon* 



