886 ME. W. HUGGINS OX THE SPECTRA OF SOME OF THE NEBULA. 



' "Durchmesser gemessen =27"." — Sciiultz ♦. 



The spectrum of this nebula consisted of one bright nebulous line of the same refran* 

 gibility as the brightest of the lines of nitrogen. No other lines were certainly seen. 



The three brighter of the enclosing stars gave the usual stellar continuous spectrum. 



Sir John Hkrsciiel remarks of these stars near the nebula, " The point to which I 

 would draw attention is the frequent and close proximity to these objects (the planetary 

 nebula)) of minute stars, which suggest the idea of accompanying satellites"'}'. 



D'AiiREST, referring to these small stars, says (in 1856), " Von den Satelliten der 

 planetarischen Nebelflecken die widergesehenen standen noch unverriick in den von 

 Sir J. Hebsciiel so sorgfaltig bestimmten Stellungen, oder kcinnen sich im Laufe der 

 letzten Vierteljahrhunderts nur sehr kleine Grossen daraus entfernt haben.". ..." Von 

 etwa drittehalb Hundert Nebeln lasst es sich sehr wahrsheinlich machen, dass eigene 

 jahrliche Bewegungen im Betrage von mehr als einer Bogensekunde nicht vorhanden 

 sind. Streng beweisen endlich liisst sich vollstiindige Unmerklichkeit der Eigenbe- 

 wegung wahrend der letzten GO Jahre bei einigen unter den planetarischen Nebel- 

 flecken "J. 



[No. 4499. 2043 h. 38 H. VI. R A. 19'' 24'" 53'. N.P.D. 81° 3' 37"-8. Considerably 

 bright ; small ; irregularly round ; well resolved.] 



"A very small roundish cluster, 40" diam., of very small stars, one brighter than the 



rest. It is like a nebula well resolved, and is a curious object Doubtful if a 



resolved clustei", or a nebula of the first class." — Sir John Herschel §. 



"Four stars in nebula, and two more on preceding edge." — Lord RosSE ||. 



" Suspect more smaller stars "^. — Lord Oxmantown. 



* Astron. Nachrichten, No. 1541. f Philosophical Transactions, 1833, p. 500. 



J Beobachtungen der Nebelflecken und Sternhaufen, p. 308. 



Some observers describe indications of the occurrence of continual and very rapid variations in the light 

 of some of the gaseous nebulae. It must not be forgotten, however, that in the nebuloe only phenomena of 

 enormous magnitude could be visible to us. Besides this consideration, in the constantly varying state of our 

 atmosphere, and in the variation in the power of the eye to appreciate minute differences of relative brightness 

 when the conditions of illumination of the object are different, we have probably a sufficient explanation of 

 these phenomena. 



M. 0. Stkuve (in 1856) says, "... the general impression that I have derived from the observations of 

 this year, has been that the central part of the nebula of Orion is in a state of continual change with regard to 

 the brightness in different parts of it. Even with the best definition, its appearances were to me on no evening 

 entirely agreeing with those on the next or any other night."- — Monthly Notices Eoyal Astron. Soc. voL xvii. 

 p. 230. 



Dr. A. ScHULTZ (in 1865) observes of No. 4234, 1970 h., "Der Nebel flammt nicht in gewohnlicher Weise, 

 zeigt aber cine anaufhorlich gleichmassige Dilatation und Contraction." And also of No. 4572, 2075 h., 

 " Momentan werschwindet die Nebulositat ganz (?) und der Nebel zeigt sich wie ein sehr reicher gedriingter 

 Sternhaufen." — Astronom. Nachrichten, No. 1541. 



§ Philosophical Transactions, 1833, p. 464. || Ibid. 1861, p. 732. 



^ This observation, and those of other nebulae to which the name of Lord Oxmantown is attached, have been 

 kindly extracted for me from the observations made at Birr Castle. 



