452 



KNOWLEDGE & SCIENTIFIC NEWS. 



[June, igo6. 



ground ckxoiil of anv nebulous light. With reference 

 to one of his " sweeps " he says, " Tlie northern end 

 of the /one, though pretty rieh in slt/rs, is yet quite free 

 from brigiitness of ground. It is as black as a coal," 

 clearly showing that his optical power could — here, at 

 least — fairly penetrate through the stellar stratum into 

 the starless void beyond. 



I'hotographs of some portions of tin- Milky Way 

 show the fainter stars as points of light on a black 

 ground devoid of all nebulositx'. .More powerful tck-- 

 scopes and more sensili\e plates will probably disclose 

 the existence of many fainter stars, but all the evidence 

 we have at present seems to point to the conclusion 

 that the utmost limit of telescopic vision will soon be 

 reached, and that the most powerful telescope which 

 man can construct will ultimately show that the stars, 

 e\('n in the richest portions of the Milky Way, arc 

 strictly limited in number. 



The general aspect of the .Milky Way seems sullicient 

 to neg'ati\e the "disc theory." The numerous con- 

 volutions, rifts, and " coal sacks " shown in the draw- 

 ings of Boeddicker and Gould and in photographs of 

 the Milky W'ay can liardlv be explained by the honey- 

 combed strui ture of a stellar disc, and one finds it 

 dillicult to resist the conclusion that the apparent 

 streams of nebulous light w hich are seen branching out 

 in many directions from the Galactic zone are reallv 

 streams of stars and nebulous matter in space, and that 

 the apparent openings or holes, known as "coal 

 sacks," are, in reality, perforations through a stellar 

 stratum ol comparative thinness rather than cosmical 

 tunnels of immeiise length pointing directiv towards the 

 earth. 



With reference to the clusters and nebuke, the 

 distance of these objects has not been ascertained; but 

 from the fact that stars, clusters, and nebuke are mixed 

 up in the .Magellanic Clouds in a space which is ap- 

 parently of a ne;u-ly globular form, we mav conilude 

 that all these diverse objects may co-exist in the same 

 region of space, and that, consequently, the nebuke are 

 not, as a rule, farther from the earth than the faint 

 stars seen in the same direction. I'liotographs of the 

 Magellanic Clouds, taken by the Harvard observers, 

 show that these objects are very rich in small stars. 

 Photographs of the large cloud show al)out 300,000 

 stars. This would gi\e about 300 millions for the 

 whole sky, if equally rich. The small cloud seems 

 still richer, as the photographs show^ about 280,000 

 stars on an area of about 10 degrees. This would give 

 the enormous total of 1,155 millions for the whole sky, 

 and it is, perhaps, the richest spot in the hea\ens. As- 

 suming a distance of 3,000 light years, I find an average 

 distance between the component stars of the large cloiad 

 of about gl years, or more than the distance between 

 Sirius and the earth; and for the small cloud an average 

 distance of about 5 years. It will he seen that both are 

 considerably less than the average for the whole sky, 

 and show that the stars in the clouds are crowded to- 

 gether. 



Seehger estimates that the limits of the Milky Wav 

 lie between 500 and 1,100 times the distance of Sirius; 

 that is (the distance of .Sirius being 8.8 light years), 

 between 4,400 and 9,680 light years.' At these dis'tances 

 the sun would be reduced to the magnitudes 15.7 and 

 17.4 respectively. As most of the .stars in the Milkv 

 \Vay are much brighter than this, and as most of them 

 are, according to Kapteyn, smaller than the sun, we 

 may, I think, reasonably i eject -Seeliger's distances as 

 excessive. Xewcomb's distances are probablv much 

 nearer the truth. 



Miniature 

 Harmonographs. 



By Charles E. Benh.wi. 



One of the chief drawbacks of the harmonograph is its 

 cumbersome character and the heavy weights required. 

 By adopting the method described in the January number 

 of " Knowledge," of making the recorder a needle point 

 attached to a light strip of paper, friction is so far dimi- 

 nished that It is possible to reduce the size of the 

 apparatus, and to make use of weights of not more than 

 lib. each. It might be supposed at first sight 

 that the avoidance of friclion which this device secures 

 could be attained just as well by counterbalancing the 

 pen lever, but this is not so, for the counter-balanced 



cgEE? 



Fig. I.— Miniature T» in-lilliptic Pendulum. 



lever if brought so near to equilibrium will bounce, and 

 prove quite unsuitable for carrying the pen that is to 

 record a continuous line. 



Fig. I shows a miniature twin elliptic pendulum of 

 very simple construction. A pendulum rod, h inch thick, 

 and 20 inches long, is mounted on gimbals at the centre, 

 and passes vertically through a hole of about 2 inches 

 diameter in a firm table. The gimbals are formed by a 

 fiat light steel ring, resting on knife edges rising from the 

 table and receiving ou its upper surface the knife edges 

 of the pendulum, at right angles to those under the ring. 

 At the top of the pendulum is a flat round table, about 4 

 inches in diameter. The pendulum weight (i lb.) slides 

 up and down the lower part of the rod and can be fi.xed 

 by the perforated nut and screw below it. 



The rod terminates in a metal cap in which is centrally 

 fixed, embedded in lead, a hanging thin steel wire (a 

 " first " mandoline string). The other end of the steel 

 wire terminates in a loop to which by means of a brass 



