ASTRONOMY FOll 1889, 1890. 123 



place tbej' gWe as the true position of the nebular line, and record the 

 differences from this mean as due to differences of motion from the 

 mean motion. The extreme difference observed between any two 

 nebulae amounted to very nearly 70 miles per second. 



It is impossible to leave this paper without a word on the accuracy 

 of the measures. The spectrum of I 6 was examined on nine nights. 

 The greatest difference of any one night's observation from the mean 

 was only 0.11 tenth-metre, or in miles per second 4.2; the mean dif- 

 ference but 0.04, or in miles per second 1.5. Such accuracy was only 

 possible by using an enormous dispersion, and it implies very perfect 

 instrumental and atmospheric conditions. But it also implies an ex- 

 treme delicacy of eye and hand in the observer ; the " man behind the 

 telescope" is in evidence. For it should be remembered that the great 

 size of the Lick telescope is no special advantage in work of this par- 

 ticular class, its high proportion of focal length to aperture being a 

 distinct disadvantage. A much smaller object-glass, with a focal length 

 of 12 to 1, would give brighter images. — (E. W. Maunder. The Ob- 

 servatory, No. 168.) 



Mr. Lockyer having published some results at variance with those 

 obtained by Dr. and Mrs. Huggius with respect to the principal line 

 in the spectrum of the great nebula in Orion, they have made careful 

 re determinations, decisively confirming their previous results : (1) that 

 the principal line is not coincident with, but falls within, the termina- 

 tion of the magnesium flame band; (2) that in the nebula in Orion this 

 line presents no appearance of being a "fluting." 



The faint star discovered in the trapezium of the Orion nebula by 

 Alvan Clark, when the Lick telescope was first mounted, has been 

 found by Barnard to be double, another star has also been detected in 

 the trapezium by Barnard, and also one of about the same magni- 

 tude (sixteenth) as the Clark star just preceding the trapezium. 



Within the ring of the well known riug nebula of Lyra six stars have 

 been found by Holden and Schaeberle with the 36inch Lick telescope 

 where but one was known before, and five new stars have been found 

 in the nebulosity. 



ASTRONOMICAL CONSTANTS. 



Refraction.— M. Radau has published in volume 19 of the Paris Observ- 

 atory An7iales a very complete memoir on astronomical refraction, which 

 deals with the theoretical as well as the practical side of the question, 

 and contains complete tables in a convenient form suitable for actual 

 computation. 



Diurnal nutation. — M. Folie's work on diurnal nutation has not met 

 with general acceptance. One of the latest discussions of the subject 

 is that by Herr Lehman Filhes, published in No. 2975 of the Astronom- 

 ische Nachrichten. 



