35^ 



NATURE 



[Azigust 9, 1888 



Mr. Hill (late assistant to Prof. Davidson), which leaves Mr. 

 Keeler free to make the necessary studies of the great star 

 spectroscope, which is one of the most important accessories of 

 the 36-inch equatorial. Mr. Barnard is assiduously observing 

 comets and nebulas with the fine 12-inch equatorial, and getting 

 the . photographic appliances in readiness to be used with the 

 great telescope. He has already discovered twenty new nebulas, 

 found in the course of his sweeps for new comets. To show you 

 some of the advantages of our situation here, I may tell you that 

 Prof. Swift, of Rochester, has a fine 16-inch equatorial by Alvan 

 Clark, and has discovered many faint nebulas by its use. Two 

 nights ago Mr. Barnard was examining some of these excessively 

 faint objects by means of the 12-inch telescope (which gives only 

 a little more than half the light of Prof. Swift's), and in the field 

 of view where Prof. Swift had mapped only one nebula Mr. 

 Barnard found three, two being, of course, new. This is due 

 not only to the observer's skill and keenness of eye, but in great 

 measure to the purity and transparency of our atmosphere here. 



"The Eastern astronomers have given up the observation of 

 Olbers's comet, which is now only about 7/100 as bright as last 

 year, but Mr. Barnard has succeeded in following it up to last 

 night, when it finally became too faint to be seen even here. 

 These observations, which are several weeks later than those of 

 other Observatories, are of real value, as they determine a larger 

 arc of the comet's orbit, and enable its motion to be fixed with a 

 much higher degree of accuracy. Mr. Keeler is just reducing 

 his observations of the faint satellites of Mars, made with the 

 large telescope during the past months. You can gain some 

 sort of an idea of the immense advantage of the great telescope 

 in such observations, when I tell you that the brightness of the 

 satellites as observed by him was only about one-sixth of their 

 brightness at the time of their discovery. We can, then, 

 make satisfactory observations of objects which are six times 

 fainter than those very minute satellites of Mars were when 

 Prof. Hall discovered them in 1877 with the great telescope 

 at Washington. I am becoming familiar with the performance 

 of the large telescope and learning how to get the very best 

 work from it. It needs peculiar conditions ; but when all the 

 conditions are favourable its performance is superb. I am, as 

 you know, familiar with the action of large telescopes, having 

 observed for many years with the great refractor at Washington, 

 but I confess I was not prepared for the truly magnificent action 

 of this, the greatest of all telescopes, under the best conditions. 

 I have had such views of the bright planets (Mars and Jupiter), 

 of nebulas, the Milky Way, and some of the stars, as no other 

 astronomer ever before had. Jupiter, especially, is wonderfully 

 full of detail that I had not begun to see before. The disks of 

 his moons can be readily noted in smaller telescopes ; but here 

 they are full and round, like those of planets. I am almost of 

 the opinion that the curve of Jupiter's shadow might be seen on 

 the surfaces, under favourable circumstances, when the satellites 

 suffer eclipse. There is reason to believe that the satellites of 

 Jupiter, like our own moon, present always the same face to 

 their planet. This can be studied here to great advantage if 

 the disks present any of the markings which are reportedby 

 other observers. 



" The Milky Way is a wonderful sight, and I have been much 

 interested to see that there is, even with our superlative power, 

 no final resolution of its finer parts into stars. There is always 

 the background of unresolved nebulosity on which hundreds and 

 thousands of stars are studded — each a bright, sharp, separate 

 point. The famous cluster in Hercules (where Messier declared 

 he saw ' no star ') is one mass of separate individual points. 

 The central glow of nebulosity is thoroughly separated into 

 points. I have been specially interested in looking at objects 

 which are familiar to me in other telescopes and in comparing 

 our views with the drawings made by Lord Rosse with his giant 

 6 foot reflector. Theoretically, his telescope should show more 

 than ours, for his collected the most light. But the definition 

 (sharpness) of his is far behind our own, as we constantly see. 

 For example, the ring nebula in Lyra is drawn by Lord Rosse 

 with no central star. At Washington, one small star can be seen 

 in the midst of the central vacuity, but here we are sure of seeing 

 three such at least. These are interesting on account of their 

 critical situation in the nebula, not simply as stars. 



" The great Trifid and Omega nebula; are wonderful objects 

 here. 'Not only is a vast amount of detail seen here which can- 

 not be seen elsewhere, but the whole aspect of them is changed. 

 Many points that are doubtful with other telescopes are perfectly 

 simple and clear here. I have always considered that one of the 

 great practical triumphs of this telescope would be to settle, 



once for all, the doubts that have arisen and that will arise else- 

 where. Now, I am sure that we shall be able to do this, and in 

 a way to end controversy. 



" Of course you understand that the period of construction 

 here is not yet quite over, though, I am thankful to say, it is 

 nearly ended. We have been making our observations, so far, 

 under great disadvantages, and now that we see the way out of 

 most of them, and look forward to work uninterrupted by 

 machinists and constructors, we begin to realize the opportunity. 

 It really takes time to understand how to utilize it in the very 

 best way. A great telescope is not like an opera-glass, which 

 can be taken out of one's pocket, and which is at once ready for 

 use. It is a delicate and a complicated machine, which demands 

 a whole set of favourable conditions for its successful use. 

 Every one of these conditions has to be studied and understood, 

 so that it can be commanded and maintained. We have been 

 busy night and day in this work, and in completing the thousand 

 arrangements and contrivances which are essential in order to 

 turn this vast establishment from a museum of idle instruments 

 into a busy laboratory, where the inner secrets of the sky are to 

 be studied. We feel sure now that in a comparatively short 

 period we shall be in full activity. In the meantime every one 

 of us is doing his best under the conditions. 



" We expect to open the Observatory to visitors every Saturday 

 night from 7 to 10 o'clock, beginning next Saturday, July 14. 



"Edward S. Holden." 



SCIENTIFIC SERIALS. 



Studies from the Biological Laboratory of Johns Hopkins 

 University, vol. iv. No. 4, June 1888. — On the life-history of 

 Epenthesis mccraydi (n. sp. ), by W. K. Brooks, Ph.D. (plates 

 13-15). In June 1887, Dr. Brooks found at Nassau, in the 

 Bahamas, a few specimens of a Hydromedusa belonging to the 

 Eucopidas, bearing upon each one of its four reproductive organs a 

 number of Hydroid blastostyles from which young Medusa? were 

 produced by budding ; a method of reproduction which has no 

 parallel among the Hydroids, if, indeed, it occurs elsewhere in 

 the animal kingdom. While in their endless diversity the Hydro- 

 medusas present nearly all imaginable phases of development, 

 yet in all hitherto recorded cases the life-history of each species 

 from the egg to the second generation of eggs is a history of 

 progression, but this Nassau Medusa is an exception to the 

 general rule ; the bodies which are carried on the reproductive 

 organs of the Medusa are true blastostyles, so that there is a re- 

 capitulation of larval stages without sexual reproduction. This 

 remarkable form had on its first discovery been referred to 

 Oceania, but is really an Epenthesis. The Medusas carry on 

 their reproductive organs campanularian Hydroid blastostyles, 

 inclosed in chitinous gonangia. These blastostyles do not multi- 

 ply by budding or from Hydroid cormi, although they produce 

 Medusas by budding. The ectoderm of the blastostyle is produced 

 by ordinary gemmation, and is directly continuous with the 

 ectoderm of the Medusa, but its endoderm has no direct com- 

 munication with the medusal endoderm, its germ-cells arising by 

 the process termed sporogenesis by Metschnickoff. — Observations 

 on the development of Cephalopods : homology of the germ- 

 layers, by S. Watase (plates 16 and 17). In this most important 

 paper the history of the formation of the germ-layers is traced, 

 and many disputed points are settled. — On the development of 

 the Eustachian tube, middle ear, tympanic membrane, and meatus 

 of the chick, by Dr. F. Mall (plates 18 and 19). Confirms Prof. 

 His's demonstration, controverted by Fol and others, that the 

 branchial clefts are not fissures. — On the branchial clefts of the 

 dog, with special reference to the origin of the thymus gland, 

 by Dr. F. Mall (plates 19-21). — On experiments with chitin 

 solvents, by T. H. Morgan. Recommends the Labaraque solution 

 (potassium hyperchlorite) as a solvent for chitin. 



Notes from the Leyden Museum, vol. x. No. 3, July 1888. — 

 Among the longer articles may be mentioned : — On the Erotylidas 

 of the Leyden Museum, by the Rev. H. S. Gorham. About 

 seventeen are new, including four for which it has been necessary 

 to make new genera. — On some new Phytophagous Coleoptera 

 from Brazil, by M. Jacoby. — On the Shrews of the Malayan 

 Archipelago, by Dr. F. A. Jentink. — On the habits and anatomy 

 of Opisthocomus cristalus, by Dr. C. G. Young. In this paper 

 there are no references to the various memoirs already published 

 on the anatomy of this bird. — On some new or little-known 

 Longicorns (Pachyte.ria), by C. Ritsema. — On birds from the 

 Congo and South- Western Africa, F. B.ittikofer. 



