Sept.. 1Q04.I 



KNOWLEDGE & SCIENTIFIC NEWS. 



211 



b\ ;;„ :...,..,: ...... ,.^,.oiued ill olhcr parts of the ^lob.-. 



In Africa, the £;enera Acrafa and Aiiuiuris have a wide 

 range, and are represented by many well-marked species. 

 While in the Indo-Malayan region the great sub-family 

 of the Diinaiiuie, all the members of whicii are rendered 

 conspicuous by their warning liveries, is a dominant 

 group. 



The accompanying photographs represent a few 

 common and very typical warningly coloured butter- 



DanaU t-dmjn<H. Ex Philippines (white and blacki. 



flies, and a glance at them will give the reader a better 

 idea of the special designs associated with inedibility than 

 could be gained from a mere description. It will be seen 

 that the aim is to produce a startling effect ; one, more- 

 over, that will not easily be overlooked or confused. 

 On contrasting such warning liveries with the tints of 

 insects which are wholly or partially protectively coloured 

 to harmonise with their surroundings, it becomes very 

 obvious that designs so different must have been pro- 



Danaia Chtyaippus. Widely distributed in Eastern Hemisphere fulvous- 

 brown, marked with black and white . 



duced in response to equally diverse circumstances. It 

 is, moreover, worthy of note that warningly coloured 

 butterflies, as a rule, differ little in the tinting of the 

 upper and under surfaces of their wings ; whereas 

 butterflies unprotected by inedible qualities, even tiiough 

 they may possess brightly coloured upper surfaces to 

 their wings, usually have them tinted beneath in harmony 

 with leaves, bark, sand or rock. Thus, as soon as they 

 settle with folded wings, their protective colouring comes 

 into play. 



Modern Cosmogonies. 



By Miss .-\gni;s Ci,i:rki;. 



X. — The Forms of Nebulae. 



.Siu \\'ii.i.i.\.M lii:KsciiEl.'s celestial surveys lirst made 

 the classification of nebuhe [)racticable. Until he 

 Iieyan grinding specula at Halh very few such objects 

 were known, and those too imperfectly for the effectual 

 discrimination of their differences. Arrangement pre- 

 supposes comparison, and comparison some variety of 

 ■specimens to be compared, which became available 

 only through Ilerschel's scrutiny. The rapidity and 

 penetrative power of his oljservations in this field 

 almost passes belief. He detected with discernment. 

 Discovery and enrolment did not satisfy him ; he was, 

 besides, keen to note analogies and contr.nsts, likenesses 

 and dissimilitudes. He could not see without ;it the 

 same time setting in order w hat he saw ; and the law 

 of order that commended itself to him was founded on 

 an evolutionary principle. The contents of the heavens 

 seemed to fall spontaneously, as he regarded them, into 

 genetic sequences ; and the neliuke with particular 

 facility. The criterion adopted was that of progressive 

 condensation. Development must clearly, he judged, 

 be attended by contraction and local brightening. 

 Diffused milky tracts represented cosmic formations in 

 their most rudimentary form ; they assumed, through 

 the unremitting action of gravity in drawing their 

 particles together, a more compact texture, riiore 

 definite shapes, and a heightened lustre. 



L5ut things ha\e changed somewhat in aspect during 

 the last hundred years. Herschel's simple rule of 

 .arrangement, although of unquestioned validity, needs 

 to be supplemented by others. Much auxiliary know- 

 ledge has been acquired since it was formulated. In 

 .ittempting to estimate the comparative antiquity of 

 nebula, we no longer depend exclusively upon one set 

 of indications. The conclusions drawn from their im- 

 mediate inspection can at least be checked by the study 

 ol their spectra and distribution. 



The .Milky Way might be figuratively described as 

 tile nursery-garden from whicli the parterres of the 

 universe are stocked. A primitive condition is usually 

 •assigned, not without good reason, to any class of 

 objects markedly tending to collect in its plane. And 

 this is the case with gaseous, or " green " neljuke. 

 .Moreover, their materials appear to be in a highly ele- 

 mentary state tif it be permissible to speak of one kind 

 of matter as more elementary than another) ; their 

 spectra including no rays due to metallic incandescence, 

 but mainly those of nebulium, hydrogen, and helium. 

 These substances, inconceivably attenuated, constitute 

 the vast irregular formations placed by Herschel at, or 

 near, the start of cosmical development. And so far 

 he has been justified by the outcome of modern re- 

 search. But he has not been justified in his descrip- 

 tion of planetary ncbukc as " very aged, and drawing 

 on towards a period of change or dissolution." For, 

 despite their determinate shape and definite boundaries, 

 they do not appreciably differ in composition from 

 iiel)ul;eof the " irregular " class, and must be reckoned 

 as, in a manner, coev.il with them. 



There is, on the whole, a concurrence of evidence 

 that gaseous nebulffi are at a very early stage of 

 growth. They are the least elaborated of sidereal ob- 

 jects ; they seem, many of them, barely to have crossed 



