22 Report S.A.A. Advancement of Science. 



Bayer, tlien drawing up his catalogue of the stars, gave it the designa- 

 tion " omicron " Ceti. Yet it was sixty years later in time before 

 the law of its variation was discovered, so unwilling were men to grant 

 that one of the immovable stars could wax and wane in a stated 

 interval, in this case in almost eleven months. 80 remarkable was 

 this first of the variable stars considered, that the men of Kepler's day 

 called it Mira — the "Wonderful. Wliat was wonderful in their day is 

 indeed commonplace in ours, for nearly a thousand stars are now 

 known to vary like Mira. Perhaps what we to-daj' deem wonder- 

 ful our descendants four centuries hence may regard as extremely 

 commonplace ! 



I mav not tarry to relate the slow march of the science of a ariable 

 stars during the two centuries following on Fabricius's discovery. 



In 1669 Montanari discovered, or redisco\ ered, the variation of 

 Algol ; but so little attention was paid to his discovery that for over a 

 centur}' no attempt was made to deal with its apparently unaccount- 

 able and irregular fluctuations. It was left to Goodricke — an English 

 amateur in 1872 — 113 years after its discovery, to explain its varia- 

 tion ; this he did b}' showing that the variation was due to the circling 

 round Algol in three days of a large dark satellite, that e\ery revolu- 

 tion eclipsed the light of the primar}'. 



The truth of this brilliant conjecture has been sufficiently proved 

 in recent 3'ears by Pickering, Vogel, Belopolsky, Campbell and others 

 from spectroscopic evidence. But to go back to our history. 



During the seventeenth century, in addition to Algol two new 

 variable stars were discovered, Avhich added to Mira, the single 

 periodic Aariable known previous to 1600, makes a total of six variable 

 stars known at the end of the seventeenth century. In the eighteenth 

 century seven new Aariable stars were discovered, four of these being 

 by two English amateurs — Goodricke and Pigott. 



Thus as the nineteenth century opened nine oi- ten stars whose 

 liglit varied Avere known to astronomers. As the nineteenth century 

 wore on, however, the number of new variables discovered steadily 

 grew. This was in part due to the new direction gi\en to observation 

 astronomy by Sir John Herschel, aIz., the careful and systematic 

 observation C)f individual stars. 



It Avas in part also due to the industrious labours of certain 

 English amateurs, notably Pigott and Goodricke at the entering in of 

 the century, and Hind, Pogson, Baxendall and Birmingham in the 

 fiftli, sixth and seventh decades. On the Continent also the illustrious 

 Argelander had giA-en to this special branch of astronomical research 

 the moulding imprint of his great genius, introducing a system of 

 obser\'ation and reduction which is more or less adopted by all Aariable 

 star observers in the present day. 



By the year 1870 about a hundred stars were known to be 

 variable — a number sufficiently large to give a dignity and an import- 

 ance to variable star Avork. Yet the search for, and examination of 

 these interesting objects was considered to he the special field of the 

 amateur, and although great names such as Argelander, Schonfield, 



