Proctor's Astronomical Lectures. 



from tho woyhe hns looked out for relation after relation, 

 ami the connection between the different relations of 

 the planetary system. Ilia researches are worthy of all 

 praise. His results are full of interest. He took the 

 paths of the asteroids and arrauaed them in 

 their order of distance, and he found cer 

 tain places whore, for some distances, there were 

 no asteroids. There are asteroids at a great number of 

 distances from the sun, extending over 400,000,000 of 

 miles, but there were gups, like those between the rings 

 of Saturn, and the way in which Kirkwood explained 

 this was: ho noted where the gaps occurred, and he 

 found them corresponding to the paths of asteroids 

 having periods commensurate with the period of Jupi- 

 ter; and a student of astronomy knows that this com 

 mensurate period must have led to great perturbation. 

 The periods of Jupiter and Saturn are as the numbers 

 two and five, and when there is a conjunction in dif- 

 ferent parts of their orbits the perturbation takes place 

 there, and they disturb each other, producing what is 

 known as tho great inequality of Saturn and Jupiter. 

 In the same way Jupiter would disturb the motion of 

 tho asteroids, if they had a period liKe his own, and 

 would prevent them from forming, his mass ie 6O much 

 greater. v And so you will find there are no 

 asteroids in those particular spaces. This 

 supports the tlieoiT that the solar system arose 

 from motion and aggregations of discrete masses ; 

 not from the contraction of a great nebulous mass. The 

 riiiss of Saturn give further evidence of the same. The 

 gap in Saturn's ring's the gap in the true ring cor- 

 responds in position to the place where this influence 

 would affect the paths of little satellites traveling be- 

 tween the rings. There on the screen before you is the 

 great Spiral Nebula as observed by Eosse, andthere you 

 see two central aggregations. As we look on 

 that nebula we find its condition unchanged year 

 after year, and recognize in the slowness 

 of any perceptible change taking plaee, evidence corre- 

 sponding to the nature of its being. Herschel and La- 

 place had a somewhat similar theory in regard to this 

 nebulous matter and the stars. Hersehel's theory was 

 based on the fant that he recognized in the heavens 

 eigus of a luminous flre gathering toward 1 certaiu centers 

 of aggregation. There are parts of the heavens where 

 he noticed that tho whole [field was lit up with a faint 

 light, and he made the strange mistake of supposing that 

 by increasing his telescopic power he could see the fire- 

 mist better. But the real fact was he could not see it as 

 well. If you want to recognize that fire-mist and 

 America istne best place to look at it have no telescope 

 at all. Use a telescopic tube, but with no magnifying 

 power. I wish I had the keenness of eyesight for 

 it. Provide yourself with a tube shaped like a tele- 

 scope, with the thinnest glass, and place disks in such a 

 position before your eye-piece so as to hide the stars of 

 any particular constellation; carefully observe the 

 heavens ant" you will have a clearer view of any fire-mist 

 than you would by the telescope. The telescope will not 

 mak luminous bodies brighter. You look at tho moon 

 with a telescope, and you think it looks brighter, but in 

 does not. The intrinsic brightness is not increased iu the 



least. By looking, ono eye through the telescope, and 

 tho other not through it. at tho moon, you will flurl that 

 although to tho naked eye the moon is smaller. It is much 

 brighter than in tho telescopic view. Toe fire-mist Her- 

 schel recognized, if it is in the heavens, should be viewed 

 without a telescope. 



ASPECTS OF THE NEBULOUS MASSES. 



I shall next pass to the gathering in of the fire-mist to- 

 ward particular parts of the heavens. We will have a 

 series of those views on the screen. These views are of 

 different kinds of uebulaj. Nebulaj may be looked upon 

 as flowers in a gardeu in different stages one springing 

 from the earth, another in full bloom, and another iu 

 seed time. There you have a nebula after it clusters, 

 and other pictures will show you the immense varieties 

 of those nebulous masses, and I would remind you that 

 the number of these nebula} is something enormous. 

 There are -as many nebula) discovered as there 

 are stars visible to the naked eye. Those pictures before 

 you exhibit different kinds of nebulae. You see the size 

 of the great nebulous mass, gathering toward certain 

 centers of aggregation. Herschel thus illustrated how 

 out ofthe great mass of fire-mist, stars might be formed. 

 There you see three stars, and now we will have another 

 picture in which still other forms of aggregations will be 

 seen. There are certain, of these nebulous masses in 

 which the stars form single clusters When examined 

 by a powerful telescope the most wouuerful complexity 

 is found in those nebulous masses. Oiher pictures will 

 show you the process of the formation of stars, There 

 you see a quantity of nebulous matter in certain parts 

 gathering toward the center. And now we will pass to 

 a series of pictures showing tho way in which these 

 nebulous matters cling around stars; and those are on 

 a larger scale, and you will see the nebulous matter 

 apparently drawn toward the various stars. 



Then, you will recognize the great difference between 

 the way in which that nebular mass is forming and 

 Laplace's theory. We shall have the room more dark- 

 ened for some time, as these nebular pictures do not 

 show sufficiently unless the room is darkened; and we 

 will have the pictures brought on rapidly one after 

 another, the next three or four of them illustrating the 

 same theory. 



In the first you perceive three rich stars, and the nebu- 

 lous matter there also is rich. There you will recognize 

 the same features. You notice the dark spors between 

 the nebular regions, and the stars always in the brighter 

 part of these nebular regions, and evidence of the 

 gathering in of it toward the stars, but we have no evi- 

 dence of Laplace's view of a rotating nebular mass. 



We will have another picture, and it will be a bright 

 one. Here the nebula would appear to have changed in 

 shape. Here is oue view of a nebula, and the next ono 

 taken by Lascell of the same nebula, differs materially 

 from it. This nebula is called Omega from its resem- 

 blance to the Greek letter. The same nebula is in the 

 picture by Lasoell, and it is so changed that 

 it is difficult to believe that it is the same 

 object. This leads us to tho idea that 

 these masses change in form. This is a view or the 

 heavens, illustrating the variation of th diff.^nt jimta 



