JUNE 3, 1915] 
NATURE 
383 

in batches by their teachers for regular instruction 
by the museum staff. This is given partly in the 
form of tours round the galleries, and partly by lec- 
tures given in class-rooms set apart for this purpose. 
Instruction is also provided for “higher-grade scholars 
and for the teachers themselves. 
In some places, as in Philadelphia, to obviate loss of 
time in taking large classes to the museum, it is now 
customary to send travelling exhibits from the museum 
to the schools. 
Further efforts to utilise the museum as a means 
of education have resulted in the formation of chil- 
dren’s museums, where collections of birds and beasts 
likely to interest children are arranged so as to convey 
some definite and easily assimilated ideas, as, for 
example, on the significance of animal coloration, or 
the shapes of animals. 
The rapid increase of vocational and industrial train- 
ing in the public schools of America, the author re- 
marks, is already creating a demand for further 
assistance from museums, which they are meeting by 
lectures on the relation of natural resources to com- 
merce and industry, and by exhibits illustrating pro- 
cesses of manufacture. It is probable that this is but 
the beginning of a phase of museum work which will 
ultimately occupy a large place in the activities of 
general museums and lead to the establishment of 
special industrial museums. 
This appreciation of the functions of museums is a 
healthy sign, and might well be emulated in this 
country, where the museum is still commonly looked 
upon as a kind of “curiosity shop.”’ Isolated attempts 
have been made on the part of many of our local 
museums to induce the public to make greater use of 
the collections exhibited for their benefit, but the 
Board of Education has yet to be educated in regard 
to the possibilities of museums. At the British 
Museum much valuable work is being done in the direc- 
tion of economic zoology, but the scope of this work 
is hampered by lack of adequate financial support. 
This very suggestive essay should be widely read in 
this country, for there can be no doubt that the educa- 
tional advantages offered by our museums are little 
kxnown or utilised by educational authorities. 
MEASUREMENT OF THE DISTANCES OF 
THE STARS! 
Fok the lecture in honour and memory of Edward 
Halley, which it is my privilege to deliver this 
year, I have chosen an account of the persistent 
efforts made by astronomers to measure the distances 
of the fixed stars. For many generations their 
attempts were unsuccessful, though some of them 
led to great and unexpected discoveries. It is less 
than eighty years ago that the distances of two or 
three of the nearest stars were determined with any 
certainty. The number was added to, slowly at first, 
but afterwards at a greater rate, and now that large 
telescopes are available and photographic methods 
have been developed, we may expect that in the next 
few years very rapid progress will be made. 
For many centuries astronomers had speculated on 
the distances of the stars. The Greeixs measured the 
distance of the moon; they knew that the sun and 
planets were much further away, and placed them 
correctly in order of distance, guessing that the sun 
was nearer than Jupiter because it went round the 
sky in one year while Jupiter took twelve. The 
stars, from their absolute constancy of relative posi- 
tion, were rightly judged to be still more distant— 
but how much more they had no means of telling. 
In 1543 Copernicus published ‘‘De Revolutionibus 
1 The “Halley Lecture’ (slightly abridged), delivered at Oxford on 
May 20, by Sir F. W. Dyson, F.R.S., Astronomer Royal. 
NO. 2379, VOL. 95| 


Orbium Ceelestium,’’ and showed that the remarkable 
movements of the planets among the stars were much 
easier to understand on the hypothesis that the earth 
moved annually round the sun. Galileo’s telescope 
added such cogent arguments that the Copernican 
system was firmly established. Among other diffi- 
culties which were not cleared up at the time one 
of the most important was this: If the earth describes 
a great orbit round the sun, its position changes very 
greatly. The question was rightly asked: Why do 
not the nearer stars change their positions relatively 
to the more distant ones? There was only one 
answer. Because they are so extremely distant. This 
was a hard saying, and the only reply which Kepler, 
who was a convinced believer in the earth’s move- 
ment round the sun, could make to critics was ‘“‘ Bolus 
erat devorandus.”’ 
Although no differences in the positions of the stars 
were discernible to the naked eye, it might be that 
smaller differences existed which could be detected 
by refined astronomical measurements. To the naked 
eye a change in the angle between neighbouring 
stars not more than the apparent diameter of the sun 
or moon should be observable. No such changes are 
perceived. The stars are—it may be concluded—at 
least two hundred times as distant as the sun. With 
the instruments in use in the seventeenth century— 
before the telescope was used for the accurate 
measurement of angles—angles one-twentieth as large 
were measurable, and the conclusion was reached 
that the stars were at least four thousand times as 
distant as the sun. But no positive results were 
obtained. Attempts followed with the telescope and 
were equally unsuccessful. Hooke tried to find 
changes in ithe position of the star y Draconis and 
failed. Flamsteed, Picard, and Cassini made exten- 
sive observations to detect changes in the position of 
the pole star and failed. Horrebow thought he had 
detected slight changes in the position of Sirius due 
to its nearness in a series of observations made by 
Rémer. He published a pamphlet, entitled “ Coper- 
nicus triumphans,” in 1727, but the changes in the 
position of Sirius were not verified by other observers, 
and were due to slight movements of R6émer’s instru- 
ments. 
Thus in Halley’s time it was fairly well established 
that the stars were at least 20,000 or 30,000 times as 
distant as the sun. Halley did not succeed in find- 
ing their range, but he made an important discovery 
which showed that three of the stars were at sensible 
distances. In 1718 he contributed to the Royal 
Society a paper entitled ‘‘Considerations on the 
Change of the Latitude of Some of the Principal 
Bright Stars.” While pursuing researches on another 
subject, he found that the three bright stars—Alde- 
baran, Sirius, and Arcturus—occupied positions 
among the other stars differing considerably from 
those assigned to them in the Almagest of Ptolemy. 
He showed that the possibility of an error in the 
transcription of the manuscript could be safely ex- 
cluded, and that the southward movement of these 
stars to the extent of 37’, 42’, and 33'—1.e. angles 
larger than the apparent diameter of the sun in the 
sky—were established. He remarks :— 
“What shall we say then? It is scarce possible 
that the antients could be deceived in so plain a 
matter, three observers confirming each other. Again 
these stars being the most conspicuous in heaven are 
in all probability nearest to the earth, and if they 
have any particular motion of their own, it is most 
likely to be perceived in them, which in so long a 
time as 1800 years may show itself by an alteration 
of their places, though it be utterly imperceptible in 
a single century of years.” 
This is the first good evidence, i.e. evidence which 
