658 



SCIENCE. 



[N. S. Vol. VII. No. 176. 



look at the same object with an instrument 

 of 36 or 40 inches aperture, under identical 

 atmosphei-ic conditions. When the seeing 

 is distinctly bad, that is, when the atmos- 

 phere is in so disturbed a state that the 

 images are blurred and unsteady, the 

 smaller instrument will assuredly show 

 all that can be seen with the larger one. 

 But with better atmospheric conditions, 

 to my eye at least, the advantage lies 

 wholly on the side of the larger instru- 

 ment, whether the object be the Moon, 

 Jupiter, Mars or Saturn. In the case of 

 the Moon particularly much fine detail 

 which I have never been able to see with 

 the 12-inch telescope is clearly and beauti- 

 fully visible with the 40-inch. I am cer- 

 tainly inclined to think that large tele- 

 scopes are greatly to be preferred to small 

 ones for work of this character. But I give 

 much less weight to my own opinion on 

 this subject than to that of Professor Bar- 

 nard, who for many years has observed the 

 planets with instruments varying in size 

 from a 5-inch telescope to the 36-inch on 

 Mt. Hamilton and the 40-inch of the 

 Yerkes Observatory. He believes a large 

 aperture to be immeasurably superior to a 

 small one for these observations. This 

 seems to me quite suificient to settle the 

 question, for it would be difi&cult to name a 

 better authority. 



One incidental advantage of such an 

 instrument as the 40-inch telescope, which 

 depends to a great degree upon the stability 

 of its mounting, is the ease and certainty 

 with which micrometrical measures can be 

 effected. Since the telescope was first ready 

 for regular use last September, Professor 

 Barnard has made with it a long series of 

 micrometrical measures, which have in- 

 cluded such objects as the satellite of Nep- 

 tune, the companion to Procyon and the 

 fifth satellite of Jupiter. The precision of 

 these measures is most satisfactory, and 

 lends special interest to an attempt which 



he has made to determine the parallax of . 

 the nebula N. G. C. 404, which is in the 

 field with the bright star /5 Andromedse. 

 This object has a definite condensation, 

 which permits its position to be accurately 

 determined with reference to a number of 

 stars in the neighborhood. A long series of 

 measures, covering a period of five months, 

 have led to the conclusion that the nebula 

 cannot possess a parallax as great as half 

 a second of arc, and, therefore, cannot be 

 nearer the Earth than about four hundred 

 thousand times the. distance from the Earth 

 to the Sun. 



Mention should be made of one more 

 interesting observation by Professor Bar- 

 nard, which would have been much more 

 difficult with a small telescope. It will be 

 remembered that in the valuable work 

 which Professor Bailey has been doing at 

 the station of the Harvard College Ob- 

 servatory in Arequipa, Peru, excellent 

 photographs were obtained of southern star 

 clusters, which show that these clusters 

 contain an extraordinary number of vari- 

 able stars. Not only do scores of stars in a 

 single cluster vary in their light, but the 

 change is exceedingly rapid, occupying in 

 some instances only a few hours. So far 

 as I know, none of these remarkable vari- 

 ations had been seen visually until Pro- 

 fessor Barnard undertook the systematic 

 observation of one of the clusters with the 

 40-inch telescope. On account of the large 

 scale of the images, he is able to distinctly 

 see stars in the cluster without confusing 

 them with others in their neighborhood, 

 and has thus been enabled to follow their 

 changes in brightness. In this way he 

 has confirmed the variability of many 

 of the stars on Mr. Bailey's photographs. 

 There are few more remarkable objects in 

 the heavens than these magnificent star 

 clusters, so many members of which are 

 subject to fluctuation in their light. Pro- 

 fessor Bailey's discovery is the more note- 



