( 524) 



tliat il is zero, The branch cO^c' of the binodal Une has thus in 

 point 0.^ a somewhat angular shape, without however an angular 

 point being really formed. 



This shape is, indeed, the preparation to the wellknown 

 form shown in fig. 14, generated in 0^ when the con- 

 jugated branch bO^b' in fig. 13 begins to intersect the 

 plait nO^a'. 



Moreover it is evident from the fact that ^^ ^^^ V-i in 

 the vicinity of the })oints 0^ and 0.^ are of the same 

 ■ order of magnitude as y/ and therefore much smaller 

 ^''^- ^"'- than y/i, that the connode 0^ will displace itself (here 

 mucli quicker than the connode 0^. 



Astronomy. — ''■The Milky iray and the star-streams:'' By Prof. J. C 

 Kapteyn. 



In a lecture, delivered before the Congress of Physicists and 

 Physicians in the month of April, I arrived at the conclusion that 

 "in passing from (he stars of the spectral type JV) (Helium-stars) to 

 those of the type A (Sirius-stars) and from these to tliose of (he 

 (ype G (solar-stars) there is a gradual change in the direc(ion of 

 the streams. 



The stream-velocity was also found to be diiferent. Owing to want 

 of materials, however, the latter result was still even more uncertain 

 than the former. Partly by tlie publication of Campbeij/s radial 

 velocities of B stars"), partly by (not yet published) observations made 

 on Mount Wilson, I have been able this summer materially to 

 diminish this uncertainty. 



It is true, that the increase of our data represents but a small 

 fraction of what is urgently wanted. Still however, so much seems 

 to have been gained already, that there is a pretty strong probability 

 in favour of the conclusion that: not only (he direction bu( also 

 the velocity of the two great star-streams gradually changes in 

 passing from type B to type A and thence to type G. 



In these circumstances I feel justified in no longer sup})ressing a 

 conclusion which was not yet communicated in my April lecture. 



In what follows, stream-direction and stream-velocity will mean 

 direction and velocity relative to the solar system, unless (he contrary 



1) 111 what follows the notations of HARVARDcollege observatocy have been 

 adopted. 

 ^) Lick Bulletin N'. 195. 



