SIR JOHN FEEDERICK WILLIxiM IIERSCHEL. 117 



him, iu overcoming what had seemed to be iusurmountable difficulties. 

 The iugeuious method by which Lord Ross afforded an equable support 

 to a large speculum, and which is now generally adopted, was then 

 unknown to him. 



The labors of Sir John Herschel in South Africa were chiefly confined 

 to different subjects of observation. Stellar astronomy, however, 

 occupied his principal attention. Two of the most celebrated ne- 

 bulae — that in the sword-handle of Orion and that surrounding the 

 variable star Eta Argus, as well as portions of the Milky Way, he de- 

 lineated with particular care. The published drawings of these objects 

 are acknowledged hy all astronomers to be the most perfect represent- 

 ations of these beautiful ornaments of the southern sky. The nebula 

 of Orion, magnificent as it is north of the equator, comes out iu much 

 grander detail in the southern hemisphere, where its great elevation iu 

 the heavens renders it comparatively free from the ill effects of an 

 impure atmosphere. During the cooler months at the Cape of Good 

 Hope, from May to October inclusive, and more especially in June and 

 July, the finest opportunities for delicate astronomical observation oc- 

 curred, and were quite equal to the observer's most sanguine ex- 

 Ijectations. Sir John remarks that the state of the atmosphere 

 in these months was habitually good, and imperfect vision rather the 

 exception than the rule. The best nights, when the stars were most 

 steady, always occurred after the heavy rains had ceased for a day or 

 two, when "the tranquillity of the images and sharpness of vision was 

 such that hardly any limit was set to magnifying power, but what the 

 aberrations of the specula necessitated." 



Upon occasions like these Sir John found that optical phenomena of 

 extraordinary splendor were produced by viewing a bright star through 

 diaphragms of card-board or zinc, pierced in regular patterns of circular 

 holes by machinery. These phenomena, arising from the interferences 

 of the intromitted rays, and produced less perfectly in a moderate state 

 of the air, surprised and delighted every one. A result of a more 

 interesting kind was obtained when the aperture of the telescope had the 

 form of an equilateral triangle, the center of which coincided with the 

 center of the speculum. When close double stars were viewed with the 

 telescope, having a diaphragm of this form, the discs of the two stars, 

 which are exact circles, are reduced to albout a third of their size, and 

 possess a clearness and perfection almost incredible. These discs, how- 

 ever, are accompanied with six luminous radiations running from them 

 at angles of G0°, forming straight, delicate, and brilliant lines, like 

 illuminated threads, reacliing far beyond the sea of view, and capable 

 of being followed like real appendages to the star, long after the orb 

 itself had left the field. 



Another optical phenomenon, arising from a peculiar condition of the 

 atmosphere, is described as " nebulous haze." The effect of it was to 

 encircle every star of the uiuth magnitude and upward with a faint 



