June 1;^, 1895] 



JVA rURE 



16^ 



above it applies to the instrument used at Allegheny), and the 

 narrow horizontal line in the lower part of the figure represents 

 an undisplaced line in the spectrum, or solar line. 



Ky Dop|)ler's principle, the displacement of any point on this 

 line is proportional to the velocity in the line of sight. The in- 

 clination of the planetary line to the solar line can be expresse<l 

 by a simple formula. It is also possible to determine the form 

 of a line in the spectrum of the ring, regarded as a collection of 

 satellites, by the application of Kepler's third law. With the 

 computed motions of different parts of the system, the dotted 

 curves in the figure were plotted. For the ordinates, how- 

 ever, twice the calculated values were taken, since the dis- 

 placement of a line, due to motion in the line of sight, is 

 doubled in the case of a body which shines by reflected and not 

 by inherent light, provided (.as in this case) the .Sun and the 

 Earth are in sensibly the same direction from the body. The 

 planetary line is drawn to the same scale, and the heavy lines 

 in the figure represent accurately the aspect of a line in the 

 S[)ectrum of Saturn, with the slit in the axis of the ring, as 

 photographed with a spectroscope having about three times the 

 dis|icrsion of the instrument used by Prof. Keeler. 



The width of .slit used is also represented in the figure. 



If the whole system has a motion in the line of sight, the 

 lines in the figure will be displaced towards the top or the 

 bottom, as the case may be, but their relative positions will not 

 be altered. 



It is evident that in making a photograph of this kind the 

 image must be kept very accurately in the same position on the 

 slit-plate, as otherwise the form of the lines shown in the figure 

 would be lost by the superposition of points having different 

 velocities. The second plate was made with s]iecial care, and 

 as the air was steadier than on the first occasion, the tiefinition 

 is on the whole somewhat better than that of plate I, altliough 

 the difference is not great. On both plates the aspect of the 

 spectrum is closely in accordance with that indicated by theory, 

 and represented in the figure. The planetary lines are inclined 

 from 3" to 4°, and the lines in the spectra of the ansie have the 

 appearance already described. 



If the ring revolved as a whole, the displacement of lines in 

 its spectrum would follow the same law as for a rotating sphere ; 

 that is, the lines would be straight an<l inclined, their direction 

 jiassing through the origin. If the ring rotated in the period 

 of its mean radius, a glance at the figure shows that the lines 

 would i>ractically be continuations of the planetary lines.- Such 

 an aspect of the lines as this would be recognisable on the 

 photographs at a glance. 



It will be seen from the foregoing considerations that the 

 photographs prove not only that the velocity of the inner •■dge of 

 Saturn's ring exceeds the velocity of the outer edge, but thai, 

 within the limits of error of the method, the relative velocities at 

 different parts are such as to satisfy Kepler's thirtl law. 



Besides (i) the proof of the meteoric conslituticm of the rings, 

 explained above, each line of the photographs gives (2) the 

 period of rotation of the planet, (3) the mean ])eriod of the rings, 

 {4) the motion of the whole system in the line nf sight. Prof, 

 Keeler has measured a number of lines on each ])late, and com- 

 ])ared the results with the computed values of the corresponding 

 quantities. 



The results for (2) and (3) from both photograjihs are : 



(2) Velocity of limb = IO-3 + 0'4 kilometres, 



(3) Mean velocity of ring = iSo + 0*3 kilometres ; 



the computed values being I0'29 and 1S78 kilometres respec- 

 tively. 



Prof. Keeler has not yet determined from his photographs the 

 motion of the whole system in the line of sight. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



CAMUK1D(;K.--Mr. T. J. I. Bromwich, Scholar of St. John's 

 College, is the Senior Wrangler of the year. There are thirty 

 Wranglers, of whom St. John's furnishes ten, ami Trinity six. 

 One Lady only is among the^Wranglers, namely Miss N. A. L. 

 Thring, of Newnham, who is placed twenty-third in the list. 



The Tyson Medal for Astronomy is awarded to Mr. .\. \'. ('.. 

 Campbell, of Trinity. 



Sir Edward Maunde Thompson, K.C.B., has been a|)pointed 

 the first Sandars Reader in Bibliography for the year 1895-6. 



NO. 1337, VOL. 52J 



The Board of Managers of the .•\rnold Gerstenbi;rg Student- 

 ship give notice that a .Studentship on this Foundation will be 

 offered for competition in 1896. 'I'he competition will be open 

 to men and wumen who have obtained honours in Part I. or 

 Part II. of the Natural .Sciences Tripos, and who.se first term of 

 residence was not earlier than the Michaelmas term of 1890. 

 The Studentship w ill be awarded to the writer of the best essay 

 on one of the six subjects printed below. The essays must be 

 sent before October I, 1896,10 Dr. .Sidgwick, Newnham College, 

 Cambridge. The Studentship will be of the value of nearly 

 ^90. It will be tenable for one year only, but subject to no 

 conditions of tenure. 



Subjects: — "A statement of the physicist's 'working con- 

 ceptions' of Matter and Motion, together with a discussion of 

 the philosophical questions to which they give rise." '" A criti- 

 cism of the diverse views that have prevailed from the time of 

 Newton onwards as to the conceivability or otherwise of Actio in 

 distans.'^ " .■\ critical examination of the doctrines of J. S. Mill 

 concerning the ground of Induction and the Methods of Inductive 

 Inquiry.'' " The limits and relations of mechanical and teleo- 

 logical explanations of natural phenomena."' "A brief historical 

 account and a critical examination of the views which make the 

 phenomena of life dependent on the existence of a special vital 

 principle." " Natural Selection considered as a special example 

 of the general principle of Evolution." 



With the view of encouraging University Extension students 

 to take up systematic courses of study, the Local Examinations 

 and Lectures Syndics have remodelled their scheme of Local 

 Lectures Certificates, and have made several other changes of 

 importance. The certificates are now arranged so as to form 

 successive steps in a ladder of continuous work, beginning with 

 the Terminal Certificate for one term's work passing through 

 the Sessional Certificate for a year's work to the Vice-Chancel- 

 lor's Certificate of Systematic Study for four years' work. There 

 is also an Afifiliation Certificate obtainable only at centres 

 affiliated to the University. This certificate is accepted by the 

 Education Department as qualifying a person to be recognised 

 as an assistant teacher. This system is thus adapted to the 

 needs of persons who merely desire a general acquaintance with 

 the subjects taught, as well as to students who are anxious to 

 make a more thorough study of them. 



The Technical Education Board of the London County 

 Council will proceeil in July next to award five of its valuable 

 Senior County Scholarships. These scholarships, which are 

 reserved as a rule for young men and women under nineteen 

 years of age, are intended to enable promising and deserving 

 students, who would otherwise be unable to afford the expense, 

 to go through a three year.s' course at a University or at a 

 Technical Institute of University rank. They are limited to 

 those candidates whose jiarenls are in receipt of not more than 

 ^^400 a ycir. The scholarships not only give free tuition, but 

 also a money payment of £(>o during each of the years that the 

 scholarship is tenable. They are primarily intended to encour- 

 age the pursuit of some branch of science, art, or technology, 

 but they may also be awarded for the promotion of studies in 

 modern languages or other branches of education. In making 

 the award, the Board takes mainly into account the record of 

 each candidate's past career and distinctions, and the evidence 

 as to ability, intlustry, and good character which the candidate 

 is able to supply. At the .same time it re.serves the right to 

 ap|ily any examination test that it may think fit. Full particu- 

 lars may be obtained from the Secretary of the Board, at 13 

 Spring (lardens, S.W. Candidates should send in their names 

 not later than June 29. 



The summer assembly 01 the National Home-Reading Union 

 will be hel<l at Leamington S|")a, from Saturday, June 29, to 

 Monday, July 8. Lectures will be given by Major Leonard 

 Darwin, M.P, , on '* The National and International .Advantages 

 of the Study of deography " : Sir Robert Ball, on "Comets" ; 

 Mr. H. Vulc OUlham, on "The Discovery of America"; Mr. 

 J. E. Marr on "The Geology of the District"; Mr. G. V. 

 Scott Elliot, on " Intere.sting Problems in Botany, suggested by 

 the Flora of the District." There will also be a conference on 

 "The Wider Education," at which the chair will be taken by 

 Dr. Hill, Master of Downing College, Cambridge. Addresses 

 will be given by Miss Moiuly, Dr. R. D. Roberts, a represent- 

 ative of the Oxford Delegacy for University Extension, Mr. T. 



