J 
J 
NovEMBER 22, 1905| 
NATORE 
relatively to the ether, there is a Doppler resistance to 
the drift utterly negligible on the sun and planets, but quite 
appreciable on meteoric dust. I confess that I am utterly 
unable to tackle the equations of motion when this force 
is taken into account, but if we make rough approxi- 
mations it seems possible that it too would lead to a 
gradual approach to the sun. The most obvious method 
of approximation in dealing with a small disturbing force 
is to omit it. Let us adopt this method here, and turn 
to another effect which can be tackled—a Doppler reception 
effect, which only comes into play when a particle is 
changing its distance from the sun. 
Imagine a particle moving in an elliptic orbit to be 
coming towards the sun. The sun pressure against it is 
slightly increased by the motion, or, virtually, gravitation 
is lessened. When the particle has swung round the sun 
and is retreating, the sun pressure is slightly lessened, or, 
virtually, gravitation is increased. That is, there is always 
a force tending to resist change of distance from the sun, 
tending, I take it, to make the orbit less eccentric, more 
circular. 
Now let us see how these forces will act on a comet, 
supposing a comet to consist of a somewhat thinly scattered 
cloud of particles of various sizes down to, say, a ten- 
thousandth of an inch in diameter. Somewhat below that 
size the particles would be repelled and never tend to 
approach the sun at all, and would be weeded out of the 
comet as it first came into our system. Let us sup- 
pose that, to begin with, the various sizes are well mixed 
up. Then at once a sorting action will begin. The direct 
sun pressure will lengthen out the year of the finer particles 
more than that of the coarser, and they will gradually 
trail behind in the orbit. 
Then the Doppler emission effect will gradually damp 
down the motion, again more markedly with the finer par- 
ticles, and they will tend to spiral in towards the sun and 
shorten the period of revolution. Then the Doppler recep- 
tion effect will tend to make the orbit ever less elliptic, 
and again with the smaller particles the action will be 
more rapid. 
In any single revolution the effect will no doubt be 
small, even on the smaller particles, but after thousands 
er millions of revolutions the particles of different sizes 
may move in orbits so different that they may not appear 
to have any connection with each other. In course of 
ages all the smaller particles, and if we have a sufficient 
balance in the bank of astronomical time even the larger 
particles, will end their course in the sun itself. 
There is one member of our system, Encke’s comet, 
which at first sight looks as if it were manifesting these 
actions even in the short time, less than a century, that 
it has been under observation. Its motion is commonly 
interpreted as a shortening of its period by 23 hours in 
each revolution of 34 years. But Mr. H. C. Plummer 
has investigated its case, and finds such difficulties, difficul- 
ties with which I need not now trouble you, that I fear 
the obvious explanation that the Doppler resistance is the 
cause must be abandoned. But though we may not notice 
the effects in any short time, I see no escape from the 
conclusion that if comets are clouds of small particles 
brought into, and made members of, our system, they at 
once begin to undergo a sorting action, the finer particles 
drawing inwards more rapidly, and ultimately ending their 
career in the sun. Possibly the Zodiacal Light is the dust 
of long dead comets. 
Where our ignorance is complete and unbounded hardly 
any supposition can be ruled out. Let me, then, in con- 
clusion, make one wild suggestion. Suppose that a larger 
planet, still so hot as to be a small sun, succeeds in 
capturing a cloud of cometary dust. Just the action I 
have been describing should go on. The cloud would 
gradually spread into a long trail, the larger particles 
feading, the smaller dropping behind and moving in, 
and ultimately we might have a ring round the planet, a 
ring tending to become more and more circular as time 
went on, with the larger particles outside and the finer 
particles forming an inner fringe. With different grades 
of dust we might have different rings. Is it possible that 
Saturn has been wild enough to have adopted this 
‘suggestion ? 
NO. 1934, VOL. 75 | 
UNIVERSITY AND EDUCATIONAL 
INTELLIGENCE. 
CampripGe.—The special board for mathematics is now 
submitting for the approval of the Senate regulations for 
part i. and part ii. of the mathematical tripos embodying 
the resolutions which were adopted by Senate on 
October 25. It has been found necessary to make pro- 
vision for the transition from the present system to the 
new one, and some temporary provisions are suggested 
for this purpose. In other respects all the regulations now 
submitted have already been published in the draft regula- 
tions appended to the report above referred to. It is these 
detailed regulations that the master of Sidney Sussex 
College and some other members of the Senate have 
announced their intention to ‘‘ non-placet.”’ 
The observatory syndicate has been considering the great 
increase in astrophysical work which has been in the 
last few years carried on in the University observatory by 
Mr. H. F. Newall. It considers the time has come when 
an assistant of university standing should be appointed 
to assist Mr. Newall, and announces the generous offer 
of Mr. Newall to find rool. a year for five years toward 
the stipend of such an assistant. The syndicate recom- 
mends (1) that for a period of five years, from January 1, 
1907, there be appointed at the observatory an assistant, 
to be entitled ‘‘ the assistant in astrophysics,’’ who shall 
be under the general direction of the Newall observer ; 
(2) that the assistant in astrophysics be appointed by Mr. 
Newall with the consent of the Vice-Chancellor, and. be 
removable in like manner; (3) that a stipend of tool. per 
annum, payable from the University chest, be assigned to 
the assistant in astrophysics, Mr. Newall having under- 
taken to augment the stipend by an annual sum of tool. 
for a period of five years from January 1, 1907. 
Two largely signed memorials have been presented to 
the council of the Senate. The first urges (1) that a paper 
or papers in natural science shall be included amongst 
the compulsory subjects of any examination which may be 
substituted for the present previous examination, and (2) 
that in the classical part of such an examination no 
separate paper in Greek and Latin grammar shall be set. 
The second requests the council of the Senate to appoint 
a syndicate to consider the advisability of instituting a 
diploma in architecture in view of the great importance 
of architectural studies, which has already been felt in 
other universities, where such studies have been success- 
fully organised. 
The following have been nominated examiners in the 
mechanical sciences tripos :—Prof. Hopkinson, Prof. W. E. 
Dalby, and Mr. C. E. Ingles; in State medicine, Dr. 
Anningson, Prof. Nuttall, Dr. J. Lane Notter, Dr. R. D. 
Sweeting, and Dr. A. Newsholme; in the diploma of 
tropical medicine and hygiene, Prof. Nuttall, Mr. C. W. 
Danields and Mr. W. B. Leishman. 
The board of agricultural studies, in consultation with 
the president of the Royal Agricultural Society, has 
appointed Major P. G. Craigie, C.B., to be Gilbey lecturer 
on the history of the economics of agriculture for three 
years from January 1. 
A syndicate has been nominated to obtain plans and 
estimates for the extension of the Cavendish Laboratory 
on the site recently assigned it by a Grace of the 
Senate. This extension has been rendered possible by the 
generosity of Lord Rayleigh, who has presented the Nobel 
prize to the University. 
Mr. Aubrey Strahan, St. John’s College, has been 
approved by the general board of studies for the degree of 
Doctor in Science. 
A University lectureship in botany is now vacant by the 
resignation of Prof. Seward. The general board of studies 
will shortly proceed to appoint a lecturer to hold office 
from Christmas, 1906, until Michaelmas, r1o1r. The 
annual stipend is rool. Candidates are requested to send 
their applications, with testimonials if they think fit, to 
the Vice-Chancellor on or before November 30, 1906. 
Mr. R. P. Gregory, of St. John’s College, has been 
appointed senior demonstrator in botany until September 
30, IQIt. 
Mr. A. Hutchinson, 
of Pembroke College, has been 
