Feb. 27, 1883.] 



♦ KNO\VLEDGE ♦ 



167 



the device painted on its surface between B and ;>'. Over 

 the outlines of tliis distorted image we carefully trace with 

 a pencil, and then tinish up our drawing in the usual way. 

 Now, bearins; in mind the principle which wc arc illus- 

 trating, it will be ijuite evident that, to an eye placed at /(, 

 the rays from our distorted picture will pass through and 



Ki.t,'. 30. 



seem as though they emanated from the corresponding 

 normal image on p ;>', so that we have only to contrive some 

 arrangement for causing the eye to occupy this jilace, and to 

 remove p pi altogether, to bee an absolutely regular i)icture. 

 This may be done by cutting out a strip of card (Fig. 37), 

 perforating it with a hole of tl.e same size ( j in.) as h, and 

 at the same height from B B', and then removing the lamp, 

 and placing it so that this hole occupies the precise position 

 that /( did. To illustrate this, we have drawn a slightly- 

 distorted view (Fig. 3G) of a fishing-boat on a moonlit sea. 

 The size of this page is the chief obstacle in the way of the 

 distortion being made greater, but the " lanky " apjjearance 

 of the masts and sails, and the elliptical moon, will indicate 

 in what direction deformation has taken place. The reader 

 must now cut out a piece of card of the exact size and 

 shape of Fig. 37, with a hole, as shown, at // ; cut it half 



Fig. 38. 



through with a penknife along the line A B, and bend it 

 back at right angles. The part shaded in our figure must 

 now be placed upon Fig. Z^, and the observer, on looking 

 through the hole It, will see Fig. 3G in its true proportions. 



At a meeting held at Liverpool on Monday, the Mayor presiding, 

 it was resolved to hold in that city, next year, an Exhibition 

 illnstrative of navigation, travelling, and commerce. The central 

 feature is to he ship constrnction and shipping industries ; but it 

 will also include exhibits illustrative of all modes of travelling — 

 ancient and modem — by land, eoa, and air, in our own ami foreign 

 countries. 



NEE DED STAR-SURV KYS. 

 By EicuMtu A. PiiocTou. 



{^Continued from p. 120.) 



I^HE bro.id general results deducibh; from my equal- 

 surface chart of 3".'1,19S stars were very striking. 

 According to the older theory of William llersehel's we do 

 not come near the boundaries of the sidereal univer.s(! with 

 such a telescope as Argelandor used. Except for some few 

 exceptionally large suns at distances where ordinary suns 

 would not be reached by such a telescope (only 2! inches 

 in diameter) there should be no greater number of stars in 

 the Milky Way zone observed with so s-niall a spacepeni- 

 trating power, than elsewhere. Even for such exceptionally 

 large suns llersehel's theory made no allowance. But what 

 is actually the case 1 These .stars which ought to bo no 

 richer on the Milky Way, are actually so much richer that 

 by their increase of wealth they positively show tho Milky 

 Way on the chart almost as clearly iis if it were mapped there ! 

 It is manifest that the circumstances of the survey by no 

 means favour such a result, but the rever.'e. Every one 

 who has ever studied the star depths knows that a star 

 which is quite clearly seen when alone or with few others 

 in the field of view, may be undisceinible when the whole 

 field of view is crowded with stars as in the richer regions 

 of the Milky Way. INtany stars then were lost in 

 Argelander's survey of the richer fields which would have 

 been well seen had they been in poorer regions. Thus 

 great as are the numbers of stars seen along the Milky 

 Way regions in my chart there would have Iteen many 

 more had the chance of catching faint stars here been as 

 great as elsewhere. This I carefully tested. Reducing the 

 power of my much larger telescope until it was about equal 

 to that of Argelander's instrument, I examined certain rich 

 galactic regions surveyed by him, and others far from the 

 galaxy, satisfying myself by using various ways of reducing 

 the field so as to exclude the blaze from many stars in the 

 former case, that whereas Argelandor and his assistants 

 could have seen but few more stars in the non-galactic parts 

 of the heavens even though they had limited their observa- 

 tions to the darkest and clearest nights, they could have 

 seen half as many stars again in the Milky Way had they 

 reduced their field of view in such sort as to avoid the blaze 

 of multitudinous stars. 



Thus marked though the increase of star wealth is in the 

 Milky Way regions as observed by ArgelUnder, the increase 

 could have been very much greater if all the stars within 

 the range of his telescope had been recorded. 



The inference from this increase of wealth on the Milky 

 Way is obvious and important. We learn that just as the 

 rounded rich regions along the Milky Way are really round 

 (i.e., roughly globular) regions of space, in which multi- 

 tudes of stars of many oi'ders of real size are strewn, so 

 the streams of the Milky Way are real stream-shaped or 

 branch-shaped regions in space in which not only the very 

 small stars as observed by the Herschels with their great 

 gauging telescopes are much more richly strewn than else- 

 where, but also stars very much larger, and well within 

 the range of very small telescopes indeed. 



Extending the principle yet further, I have made (and 

 published) investigations into the distribution of stars 

 visible to the naked eye, finding them much more numerous 

 on the Milky Way than elsewhere, and otherwise less 

 uniformly arranged than had been supposed. (In this 

 work I used scissors and a delicate balance to give the 

 areas of irregular regions of the heavens ) I even examined 

 the distribution of stars down to the fourth magnitudt; 

 only, finding it by no means uniform, and well worthy of 

 attention. 



