266 



NATURE 



[January i8, 1894 



chose as his subject " The Relations between Light and 

 Electricity." The lecture, afterwards published by 

 Strauss, of Bonn, attracted great attention in Germany, 

 and rapidly passed through half a dozen editions ; it 

 deserves to be better known in England. To students 

 of science it will be a pleasure — not unmixed with sad- 

 ness — to know that shortly before his untimely death he 

 i,ompleted the manuscript of a new work on "The Prin- 

 ciples of Mechanics." This book is already being pre- 

 pared for publication, and those who have learned to 

 value the insight and originality of the gifted author will 

 eagerly watch for its appearance. D. E. J. 



PROF. DR. RUDOLF WOLF. 



IN Prof. Dr. Rudolf Wolf astronomical science loses 

 one of her most devoted servants, and his death will 

 be deplored not only by his countrymen and the observ- 

 atory which he has directed since its foundation, but 

 by astronomers all over the civilised world. 



The services which he has rendered to astronomical 

 science have not been restricted to one branch, although 

 his name is generally spoken of with reference to sunspots. 



Born on July 7, 1816, at Fallanden, near Zurich, 

 he attended in his youth the higher schools in the last- 

 mentioned city, where he made the acquaintance of the 

 astronomer Horner, and began his first studies in mathe- 

 matics and astronomy. He then went to the Vienna 

 University in , order to study astronomy under Littrow, 

 and later to Berlin, at which place and time were 

 Encke and Poggendorf. The year 1838 saw him in his 

 home again, and this time his opportunities for astro- 

 nomical studies were few and far between, as he had 

 little time to spare, owing to his having accepted the post 

 of a teacher in mathematics and physics at the town 

 " Realschule" in Berne. In the year 1844 he commenced 

 lecturing at the university, and in 1852 he obtained his 

 Doctor's degree from the Berne Faculty, the same year 

 becoming a member of that body itself by being appointed 

 an Ausserordentliche Professor. About this time Wolf 

 busied himself with a series of fine pieces of mathematical 

 work, some of which were published singly, and others 

 in various " Fachbliittern,'' and in this year ( 1 852) he pub- 

 lished his " Taschenbuch der Mathematik, Physik, Geo- 

 diisieund Astronomic," a book which, owing to its clearness 

 of exposition, passed quickly through a series of editions. 

 One of the last pieces of work at which he was em- 

 ployed before he was overtaken by his illness was the 

 sixth edition of this small book. The year 1847 was a 

 very important one in the life of Prof. Rudolf Wolf, for it 

 was at this period that he was appointed to the director- 

 ship of the small observatory of Berne. It was there 

 that he began his well-known series of observations on 

 sunspots, which he carried on without intermission to 

 the end of his life, and which in connection with previous 

 observations led to such important results. Owing to 

 his memorable discovery of the relation between sunspots 

 and earth magnetism his name first became better known, 

 and it was more especially on this account that he 

 received his promotion and a professorship of mathe- 

 matics at the Berne University. In the year 1855 we find 

 him returning as Professor of Astronomy to the newly- 

 founded Swiss Polytechnikum, and at the same time to 

 the university in his " Vaterstadt," where at a later 

 date (1864) he received the appointment as director of 

 the newly-built observatory in which he worked with 

 great zeal to the end of his life. 



The chief work which Prof. Wolf set himself to do 

 was to obtain a continuous record of the spots on the 

 solar surface ; this led him later to examine older observa- 

 tions, and finally to compare their periods with those 

 obtained from magnetic observations. As an astronomical 

 observer Prof. Wolf was most diligent. Besides busy- 



NO. 1264, VOL. 49] 



ing himself with observations of many different kinds, 

 he made a point of regularly watching the sun's surface. 

 For fifty years, it is said, he did not allow a single day, 

 in which the sun was at all visible, to pass without 

 observing its surface with one of the observatory instru- 

 ments, or with a small pocket telescope he carried about 

 with him for that purpose. The importance of Prof. Wolf's 

 work will be gathered from the following brief historical 

 sketch. 



In 1851 Lamont, the Scotch director of the Munich 

 Observatory, in reviewing the magnetic observations 

 made at Gottingen and Munich from 1835-50, per- 

 ceived that they gave indications of a period of io^> 

 years. Sabine, in the following winter, ignorant of 

 Lamont's conclusion, undertook a similar examination 

 with very different data, and found that there was a maxi- 

 mum of violence and frequency about every 10 years ; 

 he it was, also, who first noted the coincidence betv/een 

 this result and Schwabe's sunspot period. The memoir 

 containing this remarkable communication was presented 

 to the Royal Society March 18, and read May 6, 1852 ; 

 but on the 31st /July following, Prof. Rudolf Wolf at 

 Berne, and on the i8th August, Alfred Gautier at Sion, 

 both announced similar conclusions, arrived at quite 

 separately and independently. Prof. Wolf's work began 

 then in real earnest, and he corrected Schwabe's decen- 

 nial period to one a little larger than eleven (irii), and 

 pointed out the better agreement in the ebb and flow 

 of magnetic change than Lamont's \o\ year cycles. So 

 minute and exact were his inquiries that by 1859 he 

 found that very considerable fluctuations on either side 

 of the mean period, which he had previously deduced, 

 were noticeable ; for might not two maxima rise to sixteen 

 and a half years, or sink below seven and a half years ? 

 Prof. Wolf pointed out later (1861) that the shortest 

 periods brought the most acute crises, and vice versa ; he 

 It was, also, who suggested the idea of a longer sunspot 

 period (55/, years). 



Among other branches of astronomy to which Prof. Wolf 

 turned his attention maybe mentioned that of variable 

 stars. It was in i8522that' he pointed out the striking 

 resemblance between sunspot curves (representing fre- 

 quency) and curves representing the changing luminous 

 intensity of many variable stars. Aurorse, too, received 

 Prof. Wolfs attention, and it was in the same year that, 

 as he was examining Vogel's collection of Ziirich chron- 

 icles for evidence to connect the weather with sunspots, 

 he was led to associate luminous manifestations with 

 solar disturbances. He also interested himself with regard 

 to the announcement of the discovery of Vulcan, and col- 

 lected all information of recorded appearances (.^) of what 

 were thought to be intra-Mercurian planets. 



From his youth up, Prof. Wolf had a great liking for his- 

 torical study, and was as familiar with the history of his 

 science as he was with the special branch which he made 

 his own. For several years he collected and brought to- 

 gether a great amount of " quellenmaterial," which was 

 published in the form of his " Geschichte der Astronomie." 

 Perhaps his " Handbuch der Astronomie" may be said 

 to be his best work, for there his thorough knowledge of 

 his science and his cleverness had complete scope. The 

 matter in this book is treated with both scientific ac- 

 curacy and literary ability, and is a wonderful instance of 

 his still youthful capacity for work. 



Towards the end of November last the first sign ot 

 illness showed itself, and during the first few days of 

 December quickly developed, resulting in his death on 

 December 6, at the age of 77. 



Wholly devoted to the science which he loved, and a 

 large contributor to astronomical knowledge, his name 

 will be handed down to posterity. When the principles 

 played with to-day are thoroughly perfected at some future 

 date, and we can produce perfect pictures of all solar 

 phenomena on a single plate, our future astronomers will 



