118 SIR JOHN FREDERICK WILLIAM IIERSCHEL. 



sphere of light of an extent proportioned to the brightness of the star. 

 This phenomenon presented itself very suddenly in a perfectly clear 

 sky, free from suspicion of mist or cloud, and disappeared as suddenly 

 after the lapse of about a hundred seconds. Sir John Ilerscliel stated 

 that similar nebulous affections occurred in England, but with less fre- 

 quency of coming and going. He at first suspected that the phenomena 

 arose from dew upon the eye-piece ; but repeated observations satisfied 

 him that they were atmospheric. 



Under the favorable circumstances in which he was now j)laced, the 

 opportunity of studying the grand nebula in the sword-handle of Orion 

 was eagerly embraced. He had himself delineated this remarkable 

 object in 1824. Four representations of it, differing essentially from his, 

 had been subsequently published, and it therefore became of the deepest 

 interest to discover the causes of these discrepancies, and to ascertain 

 whether in form or light a change had taken place. The splendid draw- 

 ing of this nebula, twelve inches square, is viewed with mute admiration. 

 The mysterious assemblage of suns and systems which it sets before the 

 observer is at first almost overlooked in his wonder at the j)atience and 

 skill of the artist astronomer. No fewer than one hundred and fifty 

 stars are accurately depicted, and the faint luminosity shades away on 

 the picture, as in the heavens, into the dark sky. That this marvelous 

 thing of beauty, having no relation to the stars which bespangle it and 

 no union with the stars themselves, has recently undergone or is under- 

 going great and rapid changes, Sir John did not believe. He writes : 

 " Comparing my only drawings made at epochs (1824 and 1837) differ- 

 ing by thirteen years, the disagreements, though confessedly great, are 

 not more so than I am disi)0sed to attribute to inexperience in such 

 delineations, (which are really difficult) at an early period ; to the far 

 greater care, pains and time, bestowed upon the later drawings ; and, 

 above all, to the advantage of local situation, and the verj^ great superi- 

 ority in respect both of light and defining power in the telescope at the 

 latter, over what it possessed at the former epoch, the reasons of which 

 I have already mentioned. These circumstances render it impossible to 

 bring the figures into comparison, except in points which cannot be in- 

 fluenced by such causes. Nou- there is only one such imrticular on ichich 

 I am at all inclined to insist as evidence of change, viz : in respect of the 

 situation and form of the 'nebula oblongata,' which my figure of 1824 

 represents as a tolerably regular oval. Comparing this with its jjresent 

 appearance, it seems hardly possible to avoid the conclusion of some sensible 

 alteration having taken place. No observer now, I think, looking ever so 

 cursorily at this point of detail, would represent the broken, curved, and 

 unsymmetrical nebula ia question as it is represented in the earlier of 

 the two figures, and to suppose it seen, as in 1837, and yet drawn in 1824, 

 would argue more negligence than I can believe myself fairly chargeable 

 with." 



The magnificent Catalogue of Nebuhie aud Clusters of Stars in the 



