SPIRAL NEBUL.E PUISEUX. 151 



spirals is immense, much greater than that of the mean distance of 

 the naked-eye stars, because all the visible stars inclosed in the spirals 

 are telescopic. The Hght of such stars reaches us weakened by their 

 enormous distances and doubtless by an interstelier absorbing 

 medium. 



When we consider the great number of the stars embedded in a 

 nebula like that of Ursa Major (MlOl), or that of Andromeda, it 

 seems as if we rather minimize their importance either in using tliese 

 nebulae to construct a solar system or by regarding them as the result 

 of some very improbable accidental colMsion. A single nebula is, 

 in my opinion, capable of giving birth to many stars, indeed, to many 

 clusters. By the range in theu' development, the variety of their 

 structure, the great spirals are comparable without exaggerations to 

 the milky way itself. 



I beheve that we should not derive from our latest studies the 

 theories of Chamberlain and Moulton or of Prof. Arrhcnius, all three 

 of whom interpret the spirals as due to a collision of two stars. Mr. 

 T. J. J. See has raised very strong objections against such theories 

 in his recent work, "The Evolution of Stellar Systems," a book full of 

 erudition and ingenious views, but one whose uncompromising dog- 

 matism must arouse opposition. According to Mr. See, we must 

 not present an explanation to our learned public as possible, but as 

 absolutely necessary. Is the stellar cosmogony of ^Mr. See, for he 

 has one of his own, truly one of those to which we must subscribe 

 without discussion and hold as defuiitive? He makes a spiral have 

 its birth in the meeting of two clouds of very elongated form which 

 move tlirough space with different velocities and become deformed 

 before uniting under the influence of their mutual attraction. Ea,ch 

 spiral marks the influx toward the common center of one of the 

 original clouds. 



I fear that such an explanation would be satisfactory only to 

 readers but little acquainted with the objects themselves. It is not 

 merely two concurrent spirals which we must explain, but often 

 four or five. And when we consider the parsimonious scattering of 

 matter through space, it is truly difficult to admit that upon the path 

 of the deflecting current there will appear first isolated stars, then 

 clusters of stars more and more numerous and more and more dense 

 as we approach the place of conjunction. I do not see whence will 

 be gathered the matter for these suns if there is no central condensa- 

 tion, which, according to See, would not yet have been formed. To 

 me the movement in spirals must be centrifugal and dispersive. The 

 central mass shoots out intermittently groups of stars, giving them a 

 great initial velocity, but the impulsive force acts only for a short dis- 

 tance. The final movement of the liberated stars is governed by the 



