41S 



KNOWLEDGE. 



November, 1911. 



because the explosion of the third body would he 

 of such thermodynamic intensity as to blow the s{)iral 

 to pieces. 



Whirling Coalescence of Nebulae. 

 Again, imagine that the globular nebulae strike so 



as to give us cases of whirlint 



deeph 



On the grounds of both 

 deduction and observa- 

 tion, this would seem to 

 be the general case of 

 nebular collisions. When 

 we look at the kinetics 

 of this special class of 

 impact, this deduction is 

 verv strongly supported. 

 Let us examine such a 

 case of the coalescent 

 collision of globular 

 nebulae. The pair have 

 penetrated deeply the one 

 into the other, the por- 

 tions outside the range 

 of actual collision would 

 be carried forward by 

 their own momentum, 

 but would be subjected 

 to the attraction of the 

 vast third body produced 

 by actual collision. The 

 capturing power of the 

 third bod\- would cur\e 

 these portions into a 

 double spiral. The 

 middle portion would, 

 however, be so intensely 

 heated that a good deal 

 of it would be expelled 

 both by selective mole- 

 cular escape, and by axia 



coalescence. 



Taki:n at IVv/i-o Ohs^t-^ratory Marc'i 0—7, IQIU. 



Figure 7. Nebula, y.\'.24. Comae Beren. 



Probably a high velocity case of whirling coalescence, in \ihich 



the outer parts that have not come into collision still remain as 



non-luminous dust, and so obstruct the light of the spiral. 



extrusion. Consequent 1\ 



the attraction would weaken, permitting centrifugal 

 force to act and allowing the two great tongues of 

 tire to proceed outward, as two giant arms of an 

 immense double spiral nebula. 



.\gents Modifying the Spiral. 



All kinds of modifications of the form of this 

 double spiral may be due to differences of size, or 

 difference of density, of the impacting nebulae. 

 One or both of the two colliding masses may already 



be made up of more than one centre of conden- 

 sation. In this N\ay the two arms may differ so 

 much in volume from one another, that it may 

 form a \'ast almost independent nebula at the end 

 of one of the arms : such as we see so strikingly 

 in the great nebula in Canes \'enatici, (Figure 5). 



Li the case of pre\'ious 

 rotation, the original 

 motion would give great 

 irregularit\' to the arms 

 of the spiral, and even 

 tend to give it a multiple 

 appearance. Of this 

 resultant motion we have 

 ver\- many examples. 

 Hence it seems that we 

 have but to study the 

 kinetics and kinematics 

 of the various impacts 

 of nebulae, and every 

 element of m\ stery in 

 the origin of their form 

 and structure disappears. 

 When we take into 

 account differences of 

 densitv, differences of 

 volume, differences of 

 depths of encounter, 

 differences in the stage 

 of impact, there is 

 possibh" no single form 

 amongst the hundreds of 

 thousands of those photo- 

 graphed, but \\e have a 

 clear dynamical account 

 of their evolution. Thus 

 \\e are presented with a 

 set of principles that abso- 

 luteh- explain the origin of each and everv one of these 

 exquisite celestial flouers, the glowing nebulae that 

 we find in every stage of bloom in the celestial fields. 

 In our next article we shall attempt to show that 

 bv applying the same reasoning, as here gi\'en to 

 nebulae, to the impacts of svstems similar to the 

 great clouds of Magellan, the mvster\- surrounding 

 the birth of the grand Galactic svstem we call the 

 visible universe is in like manner completely 

 dissipated, and the whole C}'cle of the eternal heavens 

 is revealed to our mental gaze. 



FOURIER'S SERIES IN THE '• ENCYCLOPAE DLA BRITANNICA." 



To those with a taste for mathematics here is fine food, 

 Fourier's invention of the series bearing his name formed a 

 landmark in Mathematical Science at the beginning of last 

 century. He shewed by their means that it was possible 

 under certain circumstances to represent any discontinuous or 

 arbitrary valued function by an even series. 



Interest is added to the study of these by knowing that they 

 have considerable application in physical science, especially in 

 the theory of heat. 



The article in the Ency^clopaedia treats the subject very 

 ably and explicitly, and gives a few well -chosen simple 

 graphical examples. 



Preceding the article on Fourier's Mathematical work is one 

 giving a short history of his political life, from which we learn 

 that P~ourier, in addition to belonging to the company of 

 illustrious men of science that France has given to the world, 

 also achieved unconnnon success as a politician, 



T, W, K, C, 



