here seen lie at different distances, and that much more clearly marked streams would be recognised if we could cut off with a veil all the stars beyond a certain distance, and obliterate altogether certain of the nearer stars. I would, however, recommend such of my readers as possess Argelander's chart to study the region around the two spaces pictured in Figs. 2 and 3; when I think the conviction will be forced upon them that there is a much closer connection between the several branches of stars seen in those regions than one would have been disposed to expect among the orders of stars Argelander has included in his charts.

Many cases occur, however, in which two streams lying at different distances appear to cross each other in the chart; and it is a somewhat noteworthy circumstance, that the disposition of five nearly equal stars in the form of a cross, thus which is very seldom met with (compared with other simple configurations) in the complete series of charts, is commonly to be noticed where two well-marked streams cross each other.

The arrangement of the stars in the large chart, as respects aggregation in certain regions and segregation from others, is sufficiently remarkable; but I have not space to dwell at length here on peculiarities of that description. Some of these peculiarities are associated with the configuration of the galactic stream of stars, presently to be briefly referred to. One, however, is so remarkable that I cannot refrain from here calling special attention to it. The Milky Way region or zone is shown in the chart to be exceptionally rich in stars (as W. Struve judged from statistical considerations); but instead of that gradual tendency to aggregation towards the galactic zone which Struve supposed to prevail, there is in many places a sudden change in the density of distribution, spaces close by the galaxy being relatively poor. But in no instance is this peculiarity so remarkably exemplified as in the part of the Milky Way near the horns of Taurus. Here we have on one side the rich fields of the Hyades and the Pleiades, and on the other rich galactic fields-properly so-called; but between these two rich regions we have absolutely the poorest region in the whole of the northern heavens.*

Extending next our range of view so as to reach the stars down to the thirteenth magnitude inclusive, we have indeed less complete surveys to consider, but yet the evidence we obtain is sufficiently distinct. The zodiacal zone has been closely surveyed by Chacornac, Hind, and others, with the

* This peculiarity did not escape the attention of Argelander, who says:— "Die absolut ärmste Gegend findet sich aber sonderbarweise nicht gar weit von der Milchstrasse entfernt, an den Hörnern des Stiers."

object of so mapping down even the fainter stars, that the asteroids which traverse this region may be the more readily recognised. In the maps thus constructed, we find star streams and star sprays as well marked as in Argelander's chart. As the same general considerations apply in this case, it will be sufficient for me to invite attention to Figs. 4 and 5; but I would recommend the student who may possess Chacornac's charts to study carefully the regions which surround the two spaces pictured in these figures.

If we pass on towards yet more remote depths, we still find well-marked signs among the stars of a tendency to form

streams and sprays. Sir John Herschel has pictured some very singular specimens of such streams, as seen in his eighteen-inch reflector during his survey of the southern heavens; and doubtless, could the fields surveyed by the elder and younger Herschel be presented in maps, so that several adjacent fields could be seen at a single view, many other instances would be added to the list.

It is scarcely necessary to add that the largest telescope ever made by man-the great Parsonstown reflector-has revealed

There is an interesting quotation at page 267 of Webb's Celestial Objects, in which Fr. Secchi describes the astonishment with which, when studying certain galactic regions, he saw spirals and curves of stars so regularly disposed as to preclude all possibility that chance distribution was in question.

even in the intricate constitution of the nebulæ the existence of streams and sprays, sometimes spiral, sometimes but slightly curved, sometimes disposed with singular regularity, at others extending in irregularly shaped branches, growing gradually fainter and fainter until they are at length lost altogether either by diffusion or through extreme faintness.

But it remains to be considered that we have strong evidence in favour of the view that the Milky Way itself is but a stream, or rather a congeries of streams of stars. The evidence on which Sir William Herschel rested his theory that the galaxy is of the shape of a cloven flat disc, was abandoned by himself

during the later years of his career as an observer; and he recognised clearly that some of those rich nodules of the Milky Way which can be seen in the northern heavens are real aggregations of stars (not vast depths along which the stars are arrayed as in a sort of procession), and that such aggregations approach in figure to the spherical form. In the southern heavens Sir John Herschel recognised galactic regions to which Sir William Herschel's later mode of reasoning could be applied even more convincingly. Now precisely the same reasoning by which Sir W. Herschel was led to regard the rich clustering regions of the Milky Way in Cygnus as spherical in form, seems to show that the well-marked portions of the galactic stream are really stream-shaped. And this view of the galaxy, which might seem to agree ill with the usual

account of this marvellous band of stars, accords excellently with the description given by Sir John Herschel and others who have most carefully studied the galaxy. More especially is it suggested by the aspect of the Milky Way in the southern heavens. For there the continuity of the zone, on which so much stress had been laid is shown to be interrupted by a broad dark rift, a feature wholly inexplicable on the theory that the Milky Way is shaped like a cloven flat disc. And over the whole region from Argo, over the feet of the Centaur, to Sagittarius and Scorpio, the Milky Way as pictured by Sir John Herschel presents an appearance far more closely according with the theory that the Milky Way in this region forms a gigantic spray of stars than with any other that has been propounded. In the northern heavens, the faintness of the Milky Way causes it to appear more uniform in structure; but even in the northern heavens, as has been well pointed out by Professor Nichol, it is only on the most cursory examination, or when the Milky Way is studied under unfavourable circumstances, that it can be regarded as a simple zone. But it is well worthy of notice that in my chart of 324,198 stars, the Milky Way reveals itself (through the mere aggregation of stars down to the 94th order) as a congeries of streams, with branching extensions, of which only the commencement can be recognised as more or less marked projections, in the best pictures of the northern parts of the Milky Way.

It remains to be noticed, in conclusion, that the nebular system also shows the most marked tendency to stream-formation when isographically charted, as in the series of charts which illustrate my paper on the distribution of the nebulæ, in Vol. xxix. of the Monthly Notices of the Astronomical Society. The tendency to stream-formation is more especially to be noticed among the southern nebula. It is worthy of remark that, whereas the southern nebular streams converge upon the Magellanic Clouds, the northern nebular streams seem to extend towards the outlying streams of the Milky Way, as it appears in my chart of 324,198 stars. The evidence of a real association between stars and nebulæ is singularly strengthened by these peculiarities of arrangement.

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REVIEWS.

POPULAR SCIENCE.*

[T is wonderful, but still it is not the less true, that scientific readers, or

readers of scientific books, are in a vastly larger proportion in the United States of America than they are here. It is perfectly amazing to be installed into the secrets of some New York publisher, and find that books, of which you hardly heard at home, treating on questions of special scientific importance, have had a sale in New York which is reckoned by thousands. Still, England is the producer, if she be not the reader, of scientific books; and in no instance is this fact more fully or admirably illustrated than in the case of the work under notice. Mr. Proctor is one of our best scientific writers, as perhaps many of the readers of this journal are aware already, but he is not only so in a truly scientific sense: he is not only thoroughly and remarkably accurate, but he possesses in a very marked degree that excellence and purity of style which are at once so attractive to the general reader, and so rarely met with in the scientific world. In the book now under notice, the reader, accustomed to Mr. Proctor's contributions to these pages, will be surprised to find that the writer has not confined his attention to purely astronomical subjects, but that physical geography, zoology, geology, physics, and physiology have each and all formed subjects of careful and advanced reading by the author. And we say this, not out of an empty desire to compliment an author who has been a contributor to our pages, but from the fact that many of the contributions, though written for some daily or other journal originally, bear on them the stamp of original thought and pure reflection. They are not essays such as we too frequently find in our journals, sparkling with bright writing, but devoid of anything like careful thought and reflection-productions which will not bear a moment's thought or reflection from the reader who is versed in his subject. Far from it, indeed. In some instances we have wondered to find them so very learned; and we have been surprised that so prolific a writer on astronomical subjects should have either the time or the inclination to go so fully into questions which have no real bearing upon the series of matters which he is engaged in studying. Of the truth of this

"Light Science for Leisure Hours. A Series of Familiar Essays on Scientific Subjects, Natural Phenomena, etc. etc." By Richard A. Proctor, B.A., F.R.A.S. London: Longmans, 1871.