2 54 



NATURE 



{_7uly 14, 1 88 1 



Suppose now F to be so large, positive or negative, as to make 

 V so great that V may be neglected in comparison with it, then 

 we may think of the cups as whirled round in quiescent air in 

 the positive or usual direction when F is negative, in the negative 

 direction when F is greater than Fj. When F is sufficiently 

 large the resistance may be taken to vary as !■-. For equal 

 velocities r it is much greater when the concave side goes fore- 

 most than when the rotation is the other way. For air impinging 

 perpendicularly on a hemispherical cup Dr. Robinson found that 

 the re-ihtance w as as nearly as possible four times as great when 

 the concave side was directed to the wind as when the convex 

 side was turned in that direction {Tramaitions of the Royal 

 Irish Academy, vol. xxii. p. 163). When the air is at rest and 

 the cups are whirled round, some little difference may be made 

 by the wake of each cup affecting the one that follows. Still 

 we cannot be very far wrong by supposing the same proportion, 

 4 to I, to hold good in this case. When F is large enough and 

 negative, F may be taken to vary as z", say to be equal to - L v-. 

 Similarly, when F is large enough and positive, F may be taken 

 equal to L':'-, w'here in accordance with the experiment referred 

 to, L' must be about equal to 4 L. H ence we mus'. have nearly — 



T) = - L f-, when t, is positive and very large ; 



7) = 4Li=, ,, negative ,, ,, 

 Hence if we draw the semi-parabala o A B corresponding to the 

 equation tj = 4 L |'- in the quadrant 17 o - |, and the semi-parabola i 



C D with a latus tectum four times as great in the quadrant 



1 o - 77, our curve at a great distance from the origin must nearly 

 follow the parabola o A B in the quadrant rj o - £, and the para- 

 bola oc D in the quadrant |o-7), and between the two it will 

 have some flowing form such as P X 11 K. There must be a point 

 of inflection somewhere between P and K, not improbably within 

 the positive quadrant \0i\. In the neighbourhood of this point 

 the curve N M w-ould hardly differ from a straight line. Perhaps j 

 this may be the reason why Dr. Robinson's experiments in the j 

 paper published in the Pliil. Trans, for 1878 were so neai'ly 

 represented by a straight line. 



FELLOWSHIPS AT OWENS COLLEGE, 

 MANCHESTER 



A SCHEME of Science and Literature Fellowships, modelled 

 ■^"^ very closely after the pattern of the Fellowship Scheme of 

 the Johns Hopkins University, Baltimore, has been organised in 

 Owens College, Manchester. The Council propose, early in 

 October next, to appoint to five Fellowships on the terms and 

 conditions following : — I. The appointment will be made by the 

 Council, after receiving a report from the Senate, not on the 

 results of examination, but after consideration of documentary or 

 other evidence furnished to them. 2. Application by persons 

 desiring to hold these fellow'ships must be made, in writing, on 

 or before October i. [In his application the candidate should indi- 

 cate the course of his previous reading and study, and his general 

 purposes with relerence to future work. 3. .The candidate must 

 give evidence of having received a sound and systema tic education 

 either in literature cr in science, such as the possession of a degree 

 of an English University, or a certificate from the authorities of an 

 English School of Medicine or Science, of good repute, showing 

 that he has passed through his cm-riculum with distinction, or, 

 in default thereof, such other evidence as shall be satisfactoi"y to 

 the Council that he is qualified to prosecute some special study 

 or investigation in the manner indicated in g 6. Finally, he 

 should produce a satisfactory testimonial of character and con- 

 duct, and should give the names of not more than three persons 

 frotn whom further information may be sought. 4. In the 

 award of the Fellowships regard will be had to the pecuniary 

 circumstances of the candidates. 5. The value of each Fellow- 

 ship will be 100/. for the academical year 1SS1-S2. In case of 

 resignation or other withdrawal from the Fellowship, payment 

 will be made for the time during which the Fellowship may 

 have been actually held. 6. Every holder of a Fellowship 

 will be expected to devote his time to the prosecution of 

 some special study, with the approval of the Council after 

 receiving a report from the Senate ; and before the close of the 

 year to give evidence of progi'ess by the preparation of a 

 thesis, the dehver^' of a lecture, the completion of some research, 

 or in some other method. He will study under the direction 

 of the Professor of the subject in which he is appointed, and will 

 be required to pay such fees as the Council shall in each case 

 determine. 7. He may be called on by the Council, after report 

 from the Senate, to render some service to the College, either as 



an occasional examiner or by giving instmction in lectures or 

 otherwise, to students in the College — provided always that he 

 shall not, during his tenure of the Fellowship, hold any reonlar 

 or salaried post as Assistant Lecturer or Demonstrator in the 

 College — but he may not engage in teaching elsewhere. S. He 

 must reside in Manchester during the academical year. 9. He 

 may be re-appointed at the end of the Session for a second and, 

 in like manner, for a third year. 10. Candidates are invited to 

 apply for appointment in any one of the following nine depart- 

 ments :—{l) Classics ; (2) English Language and Literature; 

 (3) History; (4) Philosophy ; (5) Pure Mathematics ; (6) Applied 

 Mathematics (including Engmeering) ; (7) Physics ; (8) Che- 

 mistry ; (91 Biology (including Physiology) 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, June 16. — " On Stratified Discharges. VI. 

 Shadows of Strite," by Willinm Spottiswoode, P.R.S., and J 

 Fletcher Moulton, F.R.S. 



One of the most interesting questions connected with the sub- 

 ject of stratified discharges is this : What is the physical, as 

 distinguished from the electrical, nature of the strife themselves? 

 Are they, in fact, to be regarded as aggregations of matter pos- 

 sessing greater density than the gas present in the dark spaces, 

 or are they to be considered as indicating merely special local 

 electrical conditions ? The fact of their having a definite con- 

 figuration, especially on the side which is turned towards the 

 negative terminal of the tube, that of their temperature bein<i' 

 higher than that of the dark spaces, the manner in which they 

 are affected by solid bodies, and other considerations, all tend to 

 give support to the view that the strire are loci of greater density 

 than the dark spaces. Still it can hardly be said that as yet any 

 experimental proof of this has been given sufficiently decisive to 

 decide the question conclusively. And it is in the liope of con- 

 tributing something towards the solution of this question that the 

 following experiments are submitted to the notice of the Royal 

 Society. 



The two terminals of a Holtz machine were connected in the 

 usual way with the two terminals of the tube, so as to produce a 

 stratified discharge. A narrow strip of tin-foil, or a wire, was 

 stretched along the tube opposite the column of stride. The 

 positive terminal of a second Holtz machine (in practice we used 

 for this purpose a Toppler machine) was connected with the 

 tin-foil, and the negative terminal \\ ith one (either) terminal of 

 the tube. An air-spark, or interval across which sparks could 

 pass, was interposed in the part of the circuit between the machine 

 and the tin-foil. The effect of this arrangement was this : In the 

 interval between two sparks the tin-foil and tube became charged 

 like a Leyden jar ; the tin-foil being the outer coating, charged 

 positively, and the gas inside serving as the inner coating, charged 

 negatively. When the spark passed across the interval mentioned 

 above, the jar (;'.£'. the tube) became discharged, and the electricity 

 previously held bound on the two coatings was set free. 



When the first (say the "internal") machine was not working, 

 or when it was disconnected, i.c.^ wiien no regular discharge was 

 passing through the tube, then, whenever a spark passed at the 

 second (or "external") machine, a negative discharge with its 

 accompanying Crookes' radiation took place fi-om the inside of 

 the tube next the tin-foil, and the opposite side of the tube 

 became covered with a sheet of green phosphorescence (the tube 

 being of German glass). 



When, however, other things remaining as before, a discharge 

 from the internal machine was sent through the tube, and a good 

 stratified column was produced, it was found that the green 

 phosphorescence was entirely cut off from the parts of the tube 

 opposite to the strias, while on the parts opposite to the dark 

 spaces it remained, in the form of phosphorescent rings, as 

 brilliant as before. The experiment was repeated with various 

 tubes with various degrees of strength of current, and with 

 various densities of gas (produced by heating a chamber of 

 potash in connection with the tube). It may be added that 

 when, as is sometimes the case, through greater exhaustion, the 

 striie became feebler in illumination and less compact in appear- 

 ance, the shadows cast by them lost proportionally in sharpness 

 of definition and in completeness of extinction of the phosphor- 

 escent light. 



The brilliancy and definition of the phosphorescent rings may 

 be increased by inserting a small Leyden jar in the circuit, care 

 being taken that the jar shall discharge itself completely each 

 time. If this is not the case the main discharge is followed by 



