566 
NATURE 
[Oct. 14, 1886 
been detected by Laplace’s commentators, but the secu- 
lar acceleration occupies quite a distinct position. It 
must be remembered that the calculations of Laplace 
appeared to render a physical explanation of a remark- 
able phenomenon. But when this calculation was shown 
to be seriously wrong, it followed that the cause of the 
secular acceleration conjectured by Laplace was inade- 
quate to explain the observed facts. The labours of Adams 
thus reopened the breach between the observations and the 
theory. The variations in the eccentricity of the earth’s 
orbit will account for part of the secular acceleration. The 
other part has to be accounted for in a different way. 
The theory of the tides seems to offer an explanation of the 
discrepancy. Owing to their incessant action the period 
of the diurnal rotation has been slightly elongated, and 
this effect, when duly taken account of, seems to remove 
the margin between the theoretical and observed values 
of the secular acceleration. This margin has indeed a 
singular interest in the recent theory of tidal evolution, 
inasmuch as it affords us the only measurable indication | 
we have of the effect of tides on the earth’s rotation. 
The splendid shower of shooting-stars that occurred | 
in November 1866 fixed the attention of astronomers on 
every part of the theory of these bodies. We were thus 
taught much concerning them, but for one of the most 
recondite parts of their theory we are indebted to the | 
It had been known that the | 
labours of Prof. Adams. 
great displays of the Leonids (for so these shooting-stars 
are called) take place every thirty-three years. From the 
year 902 down to the year 1866 many of the successive 
thirty-three-year periods witnessed the great shower, and 
records of a considerable number have been handed 
down to us, 
These minute bodies must revolve around the sun, each 
pursuing its orbit in accordance with the laws of Kepler. 
It became of interest to find the size and shape of this 
orbit, as well as its position. Certain features of the 
orbit are readily determined. The recurrence of the 
shower on a particular day of the year gives one point in 
the path of the meteors. The direction of the radiant 
gives a tangent tothat path, and therefore its plane. The 
sun, of course, lies at the focus, and only a single further 
element—the periodic time—is requisite to complete 
our knowledge of the orbit. We are indebted to Prof. H. 
Newton, of Yale, for his careful discus sion of this subject. 
He had shown that the choice of possible orbits was 
limited to five. There was first the great oval orbit, in 
which we now know the meteors do revolve every 33} 
years. There was next a nearly circular orbit, with a 
periodic time a little more than a year; another similar 
orbit, in which the periodic time would be a few days 
short of a year; and there were also two other smaller 
orbits. Prof. Newton had also indicated a method by 
which it would be possible to discriminate the true orbit 
as one of these five. The mathematical difficulties of 
this method were no doubt great, but they did not baffle 
Prof. Adams. 
In the Monthly Notices for April 1867, p. 247, will be 
found the paper in which he announced his solution of 
the problem. The orbit of the meteors is not fixed, but 
every time the great swarm comes round, the node is 
found to be 29’ further on in the direction of motion. The 
effect of thisis shown in the gradual alteration of the date 
of recurrence of the shower. The only influence known 
to us which could account for this change of the plane, is 
the attraction of the other planets. The problem, then, 
may be placed in this shape. A certain specific amount 
of change ofthe node takes place. The theoretical change 
can be computed for all the five different orbits, and 
Prof. Adams undertook to find it. The difficulty prin- 
cipally arises from the high eccentricities of some of the 
orbits, which rendered the more familiar methods of 
calculation inapplicable. After many months of labour, 
Prof. Adams, aided by his assistants in the Cambridge 
| Observatory, completed his work. He showed that if the 
meteors revolved in the large orbit with the periodic time 
of 33+ years, the perturbations of Jupiter would account 
for a change to the extent of 20’. The attraction of 
Saturn would augment this by 7’, and Uranus would add 
1’, the effect of the earth and the other planets being in- 
sensible. The joint effect is thus 25’, which may be 
regarded as practically coincident with the observed value 
determined by Prof. Newton. The great orbit was thus a 
possible path for the meteors, but to complete his dis- 
covery Adams had to show that neither of the other four 
orbits could experience the same perturbation. This, too, 
he succeeded in demonstrating: he showed that in no 
one of the other orbits could the change exceed 12’. Thus 
the orbit of the Leonids was discovered. 
Those tremendous powers of calculation which have 
been exercised on the heavenly bodies with such signal 
results have also been occasionally applied in various 
other directions. The discoverer of Neptune has found 
relaxation from the labours of physical astronomy by little 
calculations on which we must gaze with astonishment. He 
has had the curiosity to compute the sums of the recipro- 
cals of the first thousand numbers to 260 places of deci- 
mals. We have such confidence in the accuracy of Prof. 
Adams that we have not thought it necessary to repeat 
this calculation! He has also taken the trouble to 
calculate thirty-one of Bernouilli’s numbers beyond the 
point that previous calculators had attained, and he has 
expressed each of them both as vulgar fractions and as 
decimals, The sixty-second Bernouilli, the last computed 
by Adams, runs to 11! places, where fortunately for 
astronomy the appearance of a recurring figure has ter- 
minated this inquiry. 
Need it be added that on Prof. Adams every honour 
which science can bestow has been conferred. We have 
| now the pleasure of enriching our list of Scientific 
Worthies by the addition of his portrait. Ro Sahs 
Catalogue of the Birds in the British Museum. Vol. 
XI. Fringilliformes : Part II]. Containing the Families 
Cerebide, Tanagride, and I[cteride. By Philip Lutley 
Sclater. (London: Printed by order of the Trustees. 
1886.) 
R. GUNTHER and the authorities of the Natural 
History Department of the British Museum are to 
be congratulated, first, on having sought, and next on 
having secured, the services of Mr. Sclater for the execu- 
tion of the eleventh volume of their “Catalogue of 
Birds.” The principal group of which it treats is one 
that has been, for five-and-thirty years or more, the 
es 
