August 1, 1895.] 



KNOWLEDGE. 



179 



preceding division of the leg (Fig. 5, b). This peculiarity 

 alone gives the foot a strange appearance, reminding one of 

 the curiously elongated ankle bones in the hind leg of the 

 frog ; but this is not all, the second joint is attached to 

 its predecessor in an entirely exceptional way. As a rule, 

 the various joints of an insect's foot, numbering from two to 

 five, move but slightly upon one another at their hinges, a 

 little motion on the part of each joint thus causing the 

 whole foot to assume a regular curve. But in these Ultle 

 beetles the second division of the foot is attached to the 

 first by a socket joint, which gives far greater freedom of 

 motion, and one may often see the outer half of the foot 

 bent at right angles to the rest and seeming as if it were 

 dislocated. 



But the most astonishing peculiarity of all is that which 

 characterizes the hind legs of the genus Psi/Uiodis (Fig. 5, c), 

 a set of robust, long oval insects, one of which is de- 

 structive to hops. The tarsus of the hind leg has the same 

 elongated basal joint as Thyamis, and the same tendency 

 to bend the outer part at right angles to the rest ; but it 

 adds to these the further pecuharity that the foot is not 

 attached to the apex of the tibia (as is almost universally 

 the case, not only amongst beetles, but also amongst 

 insects of other kinds), but is inserted on the outer side 

 some little distance before the apex, so that the end of the 

 tibia projects considerably beyond it, thus giving the leg 

 an awkward and, indeed, malformed appearance. The 

 muscles which move the foot have a great 

 tendency to contract suddenly, and cause the 

 foot to spring back against the leg in a way 

 which reminds one of the elevation of a 

 drawbridge, and is very provocative of irrita- 

 tion and impatience on the part of the col- 

 lector who wishes to set his specimens neatly. 

 No doubt these various oddities of structure 

 in the tibiae and tarsi are connected with the 

 bending of the legs under the body for the 

 purpose of leaping ; but as they are not 

 universal in the group, they can scarcely 

 be essential to the habit. For example, the 

 notch on the hind leg of Phctroscdis is also found on 

 its intermediate legs, which are not bent under the body, 

 nor used in leaping. It is also found on the hind legs of 

 other plant-eating beetles, which have no power of leaping 

 at all. Altogether, therefore, it is not easy to see what 

 is the exact explanation of the presence and variety of 

 these irregularities in the hind legs of leaping beetles. 



cases it is impossible to attribute to an effect of chance ; t 

 the '• Triple Nebula," described by Dr. Max AVolf [Astro- 

 nomische Xarhruhten, Xo. 3214) ; the dark lanes to which 

 Mr. Ranyard drew the attention of astronomers, and of 

 which Mr. E. W. Maunder has given an explanation 

 (Knowledge, February, 1895), which cer(ainly appears to 

 be plausible. 



Nevertheless, the examination of these admirable photo- 

 graphs gives rise rather to hypotheses and reflections, 

 than to conclusions of which the evidence is clear and 

 striking. As long as we are unable to turn this evidence 

 into actual numbers, there will always be some astro- 

 nomers who will refuse to accept it — Proctor had some 

 experience of this I — and in reality it is fortunate that it is 

 so, as perhaps in no branch of astronomy is there so much 

 danger of arriving at premature conclusions, as in investi- 

 gations concerning the " Structure of the Heavens.'' Thus, 

 on the one hand, the researches of Struve, Gould, Eistempart, 

 Kapteyn, and others, ; tend to the admission that relatively 

 bright stars may be distributed fairly evenly around a 

 small mass, of which our sun would form part ; and, that by 

 general consent the Milky Way, properly speaking, may 

 be represented very nearly in the annular form. But 

 on the other hand, the examination of photographs, as 

 well as the careful study of the aspect of the Milky Way 

 with the naked eye, will show that this hypothetical 

 " ring " must possess an extremely complicated structure, 



4o^ 



Fia, 1.- 



Iso 



ON THE DISTANCE OF THE STARS IN THE 

 MILKY WAY. 



By C. Eastox. 



THE perfecting of celestial photography, due to the 

 patient and ingenious efforts of Messrs. Henry, 

 rioberts,Wolf,Barnard,Russell and others, isrightly 

 considered the chief glory of modern astronomy. 

 Thanks to the late Mr. A. Cowper Ranyard, the 

 readers of Knowledge have always had the first-fruits of 

 the results obtained by these savants, and numerous photo- 

 graphs, in particular of the Milky Way, have been repro- 

 duced for their benefit in this magazine. 



These photographs of the Milky Way often show 

 extremely interesting details. I need only mention here 

 ihe mhubmties, which in many cases are certainly real ;' the 

 curious arrangement of the stars in dlipscs, which in many 



•See especially the photograph obtained by Dr. Isaac Eoberts, 

 of H.V. 15 — •' A Selection of Photographs, kc," plate -io. 



x/x ■"' 



photic lines, indicating the intensity of the ililkv Way (Pannokoek). 



and that it is composed of a large number of groups or 

 stellar strata, where a certain process of agglomeration 

 already appears to manifest itself, but which strata seem 

 to superpose themselves in the direction of the visual ray. 



There is nothing to indicate whether in general these 

 groups are relatively near to each other, or whether they 

 may be, on the other hand, marshalled at enormous 

 distances one after the other in the direction of the line of 

 sight, distances which, even when compared with the 

 distance separating us from the nearest of these groups, 

 may be tremendous. I hope that the researches of which 

 the results are here given may throw a little light on this 

 latter question. 



The study of the distribution of the stars in space would 

 have made a great stride if the apparent distribution of the 

 stars of each separate order of brOliancy on the celestial 

 sphere were known. Prof. Holden, after comparing the 

 results of the star gauges one with another, says (PiM. 

 ^tVashiurn <>lis. II. I: "If these difl'erences m-n, n-o, 

 etc. — between the numbers of stars belonging to each 

 nominal magnitude m, n, etc., as shown by the gauges — 

 be platted separately, the eye can determine whether each 

 group is affected by a clustering power peculiar to itself, or 

 whether the same cause is apparent in the configuration of 



t Compare Iloldcn, Monthly Notices, Vo'. L. ; Wesley — Know- 

 ledge, August, lS9i; see in particular the photograph of the C'yngi 

 region — Knowledge, December, 1891. 



X See article on the work of Prof. Kapteyn (Knowledge, June, 

 1893), and Mr. Gore's article in the January number, 1893. 



