RECENT RESEARCHES RELATIVE TO THE NEIBUL^. 305 



and particularly interesting nebula is situated at 109^ 12' of right ascension, 

 and 29^ 45' of north declination. M. Lasscl has represented it in Fig. 9 of 

 Plate XI, accoinpaayiag his m';njir, pibli-ihed in vol. xxiii of the quarto 

 collection of the Astronomical Society of Loudon. The two components of tho 

 nebula are very distinct, though their mutual distance is at present but 28 

 seconds; but they are difficult to be seen when the threads of the micrometer 

 are illuminated. A very small star is found between the two, exactly in tho 

 same place where M. Lassell. observed it ten years ago. M. d'Arrest Avill tako 

 occasion, when his labors on this subject arc completed, to cite some other 

 analogous cases of change of relative position in double uebulce. His pro- 

 sumption, in the mean time, from what he has been able thus far to discern, is, 

 that there will not be found in any of these groups of nebulai as short periods 

 of revolution as those which have been verified in the case of some of the 

 double stars. 



Finally, M. d'Arrest reports a small number of cases where, by comparing a 

 nebula with some small star near it, and repeating this comparison at the end 

 of a certain time, he has been able to verify slight differences of distance or of 

 position, which might indicate a proper movement in one or the other of ^hoso 

 bodies. 



I here terminate this short review, in which I have been able to give but a 

 rapid glance at the present state of observation iu respect to one of the most 

 difficult and least advanced parts of astronomical science.* 



Post scriptujn. — M. d'Arrest has just announced, in No. 1378 of the A. N., 

 that he has recognized in the constellation Taurus the existence of a second 

 nebula of varisible brightness. 



*I ought here to correct an error, pointed out to me by Dr. Hirsch, ■which I committed in 

 my notice on the observatory of Neufchatel, inserted iu the number of the Archives for last 

 July, volume xiv, p. 224. It is not M. Hirsch, but Professor Kopp, of Neufchatel, who 

 forms part of the meteorological commission instituted by the Helvetic Society of Natural 

 Science. 



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