APRIL 29, 1897 | 
NATURE 
621 
The hyperbola is, of course, the easiest to produce, and the 
parabola the most difficult. Some device for regulating the 
initial velocity and aim would be conducive to more uniform 
results. 
Polarisation of the steel ball is apt to give trouble, and I 
have obtained some repulsion orbits where the ball turns back 
before reaching the centre, which are very pretty, but not de- 
sirable when one is trying to illustrate central attraction. Soft 
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iron balls would be preferable to steel on this account ; but they 
are not on the market, so far as I know, and the others answer 
the purpose well enough. 
[Supplementary Note——With a very powerful Rhumkorff 
magnet, belonging to the Massachusetts Institute of Technology, 
I have caused the ball to gyrate in a vertical plane about the 
poles, notwithstanding the perturbating influence of gravity. 
This elimination of the supporting plane makes the conditions 
Bic: 4s 
a little more like those existing in the case of plantetary bodies 
moving in space ; but the motion is so rapid that it is difficult 
to see the form of the curve, and no permanent record is left : 
moreover, the curves are distorted by the downward pull of 
gravity. 
The two conical pole-pieces of the magnet were brought close 
together, creating a very intense field, and the ball was dropped 
from elevations varying from six inches to a couple of feet at 
NO. 1435, VOL. 55] 
different distances from the vertical plane joining the poles. 
Usually the ball flies either directly to the poles, or moves in a 
path similar to some one of those shown in Fig. 3 (the pole 
being seen end on); but on several occasions I have succeeded 
Inciusing it to perform two or three complete revolutions, as 
shown roughly in Fig. 4.] R. W. Woon. 
UNIVERSITY AND EDUCATIONAL 
INTELLIGENCE. 
CAMBRIDGE.—Mr. Sidney Colvin has been appointed by the 
Council of the Senate a Trustee of the British Institution 
Scholarship Fund, in the room of the late Prof. Middleton. 
The subject for the Adams Prize for 1899 is ‘‘ The Theory of 
the Aberration of Light.” The prize is open to all graduates 
of the University. Essays must be sent to the Vice-Chancellor 
by December 16, 1898. The value of the prize is about 2002. 
_ Sixteen candidates have passed the examination in Sanitary 
Science, and will receive the University’s diploma in Public 
Health. 
The annual prize for an essay on an archeological subject 
offered by Newnham College has been this year awarded to Miss 
R. E. White (first class, Classical Tripos, 1895); the subject 
was ‘‘ Women in Egypt under the Ptolemies.” 
It is understood that the syndicate on degrees for women, 
whose report was referred back to them for reconsideration, have 
agreed to adhere to their recommendations. The voting on the 
scheme in the Senate is expected to take place about May 20. 
An active canvass for and against their proposals is being con- 
ducted by Committees in Cambridge and London. 
Ir has been decided to transfer the administration of the 
grants to schools in Scotland for science and art to the Scotch 
Education Department. The details of the transfer will be a 
matter of departmental arrangement. 
Tue Legislature of the State of New York has passed a Bill 
authorising the appropriation by New York City of two anda 
half million dollars for the purpose of erecting the new public 
library to be built on the corner of Fifth Avenue and West 
Forty-second Street, and the Mayor has approved the Bill ; so 
that the city is pledged to execute the work. 
Tue following gifts and grants to educational institutions in. 
the United States are announced in Scéence :—The Shefheld 
Scientific School of Yale University receives 25,000 dollars by 
the will of Mrs. Sarah Van Nostrand.—The department of 
natural history of Vassar College will receive about 25,000 
dollars through the settlement of the will of the late Jacob P. 
Giraud.—A Bill before the Texas Senate appropriates for the 
State University 35,000 dollars for 1897 and 85,000 dollars for 
1898, and in addition 42,000 dollars annually for the medical 
department. 
SOCIETIES AND ACADEMIES. 
LONDON. 
Royal Society, April 8.—‘‘ The Production of X-Rays of 
Different Penetrative Values.” By A. A. C. Swinton. Com- 
municated by Lord Kelvin. Received March 24. 
If the X-rays coming from a focus tube of the ordinary type 
be observed with a fluorescent screen during the process of 
exhaustion, the penetrative value of the rays is found to change: 
as the exhaustion proceeds. At less than a certain degree of 
vacuum, no X-rays are produced. As the vacuum increases, 
X-rays commence to show themselves, but of a quality that will 
do little more than penetrate the backing of the screen. At 
higher vacua the rays become more penetrative, and show the 
shadow of the bones of the hand. The point is next reached 
when the flesh of the handis very transparent, while the bones 
are still quite opaque. At higher vacua than this, the bones 
become more and more transparent, till at length, at the very 
highest vacuum at which the discharge will pass, the bones 
become nearly as transparent as the flesh, while the whole hand 
throws but a very faint shadow on the screen. 
Similar effects can be produced with a constant vacuum by 
gradually increasing the power of the Rhumkorff coil, or by 
varying the resistance of the tube by means of a magnetic field, 
the X-rays being most penetrative with great electrical power 
