AuciusT 1, 1896.] 



KNOWLEDGE 



185 



at the other extreme is S Antliffi, viz., Od. 7h. 46m. 

 and O'C magnitude. 



As to the distribution of the variables in space, as we 

 know them at present, one hundred and eightj-one are in 

 the northern hemisphere, and one liuudred and sixty-two in 

 the southern. We have prepared maps of these on an equal 

 surface projection, and on the same scale as the maps in 

 Proctor's " Universe of Stars." The Milky Way is shown. 

 In the northern hemisphere eighty-seven stars are either on 

 or near the Milky Way, showing an evident connection 

 with it. As the area of the Milky Way in the northern 

 hemisphere is certainly not so much as one-fifth of the 

 hemisphere, it is evident that far more variable stars are 

 on it than should be, if they were evenly distributed over 

 the sky. There seems a paucity of stars in the hours 9 to 

 U of E.A. 



In the southern hemisphere there is a "nest" of 

 variables in about 16h. of R.A. and 20'^ declination, 

 and another (evidently connected with the Milky 

 Way) in lOh. 11. A. and declination 60\ These 

 aggregations might be due to the fact of a search 

 of an investigator being confined to a limited part 

 of the sky. On the whole the connection with 

 the Milky Way does not seem so marked as in the 

 northern hemisphere. In the hours 1 to 4 of 

 K.A. there is a paucity of stars, and there is not 

 a single star in hour 11." 



Now comes the plain question, what is the 

 meaning of the variable stars '? This is a hard 

 nut to crack, and Class I., or the temporary stars, 

 is perhaps the hardest of all to understand. 

 Scientific men seem doubtful at present whether 

 the outburst of light which we call a new star is 

 due to an increase of heat and light in the star 

 itself, or to a collision between the star and 

 another body, whether solid or meteoric. 



The various papers published in the scientific 

 periodicals on the new star T Aurigse, which 

 appeared in 1892, show what different ideas 

 prevail on the subject, and we quote some of them 

 briefly. The Rev. W. Sidgreaves and Prof. 

 Campbell think the phenomena of this star were 

 produced in a single body. Dr. Huggins believes 

 in Klinkerfue's and Wilsing's theory, viz. : two 

 bodies travelling in opposite directions swing 

 round, and tidal disturbances come in which 

 bring about eruptions of the hotter layers of 

 matter from the interior. Miss Clerke agrees 

 with this. Mr. Maunder put forward the theory 

 that a long and dense stream of meteors 

 was travelling towards a star and rushed into or just 

 grazed it. Mr. liauyard explained the Nova as a small star 

 moving away from us through a nebula which was moving 

 towards us. Vogel thinks the Nova was produced by an 

 encounter of a heavenly body with several others. Prof. 

 Pickering suggests the phenomena as due to an outbreak 

 of eruptive prominences on an enormous scale. 



I do not mean to say that these are the views of the 

 above-named at the present time, for our knowledge is 

 evidently in a transitory stage, and views modify them- 

 selves rapidly as fresh discoveries are made. Enough 

 has been said to show that it is a difticult matter to explain 

 a new star. 



Then come the long-period variables. Hero it is 

 presumed the variation in light must take place in the sun 

 itself, and Dr. Brester has recently enounced in this 

 journal what appears to bo a satisfactory theory to account 

 for the increase and decrease in light. 



* lu rc'prodin.-tiuii tlio iiuip^ luive been rL'diK-oi,i uUL'-lmit' liiu'iir. 



The question of the interpretation of shift in the lines of 

 a stir's spectrum is discussed by Dr. P>rester, and he does 

 not think it can always be attributed to motion in the line 

 of sight. Such shift may be produced by changes of 

 pressure, temperature, chemical combinations, etc. la 

 fact, the conditions under which gases, etc., exist in celestial 

 bodies are so utterly difi^erent from what we can arrange 

 in our laboratories, that it is necessary to be very cautious 

 in interpreting a spectrum. It is, however, plain that 

 motion in line of sight, when really existing, can be easUy 

 detected in the spectroscope, for Vogel observed Venus, 

 and found that the observed (spectroscopic) velocity in line 

 of sight only differed from the calculated velocity by 0'4 

 English miles per second. 



The irregularly variable stars may, in many cases, be 

 taken to be peculiar cases of Class II., but perhaps more 

 difficult to explain. 



It seems that the change in short-period variables like 



The Variable Stars, Northern Hemisphere. Algol Stars thus : 



X or W Saglttarii or S Sagittie is due to an orbital cause : 

 a dark companion revolving round a bright central star, or 

 vice vern:!. But it is difficult to account for the iiraJiitil 

 change in the light all through the period. The extreme 

 regularity with which such stars go through hundreds and 

 thousands of their phases is a well-marked feature. Other 

 stars, like 3 Lynr, are different. Vogel tliinks the spectrum 

 of /8 Lyr.'c is duo to transiting of two bodies of unequal 

 brilliancy in an elliptical orbit whoso piano is in line of 

 sight. When tlie less brilliant body occults the brighter, 

 the principal minimum takes place. The equal maxima 

 " occur when the bodies are side by side, at right angles 

 to the line of sight. The second minimum occurs when 

 the brighter body occults the darker." This theory might, 

 perhaps, also cover a star like W Sagittarii, if the com- 

 ponents are of nearly equal size and brilliancy. 



Lastly come the Algol variables, abjut which much has 

 been written. \'oger3 theory of an opaque satellite revolv- 

 ing round the bright star in the piano of bight, and 



