FEBRUARY I1, 1904] 
of the moon and of the sky at various distances from it, to 
be compared, and a range of more than seventeen magni- 
tudes was found to exist between the extreme values 
obtained. During the period covered by the report Mrs. 
Fleming classified the spectra and measured the light of 
3506 stars, situated south of declination —60°, for the 
Southern Draper Catalogue. It is hoped that this zone will 
be completed shortly, and a catalogue containing nearly 
4000 stars, all fainter than the ninth magnitude, published. 
A large number of photographs have been obtained with 
the 13-inch Boyden and the 8-inch Bache telescopes at 
Arequipa, and a number of excellent light curves of Eros 
(from March 30 to August 19), showing a range of 05 
to 1-0 magnitude, were obtained with the former instru- 
ment by Prof. Bailey. Four hundred and thirteen photo- 
graphs, including eighty-seven of Eros, were obtained at 
the same station with the Bruce photographic telescope. 
The meteorology of the upper air has been studied at the 
subsidiary observatory at Blue Hill, where fifteen kite 
flights, twelve of which were the monthly flights for the 
international series, were performed. The average height 
above sea-level attained by the meteorograph was 6450 feet, 
and the maximum height was 12,070 feet. 
It is hoped that in a few months the Revised Harvard 
Photometry, containing the photometric magnitudes of all 
stars brighter than magnitude 6-5, about go000 in all, 
together with the spectrum class of each star and its desig- 
nation in other catalogues, will be published. 
A set of fifty-five 8” x10” contact prints from the original 
negatives, taken with the Harvard and Arequipa anastig- 
matic lenses, which cover the whole sky and contain all 
stars down to the twelfth magnitude, may be obtained by 
astronomers from the director for the sum of 15 dollars. 
Tue Direct AND RETROGRADE RoTaTIONS OF THE PLANETS. 
—In a paper communicated to No. 3925 of the Astronomische 
Nachrichten, Prof. W. H. Pickering discusses the various 
theories which have been promulgated in explanation of the 
direct and retrograde rotations of the planets. Dismissing 
the theories of Laplace, Kirkwood, Faye and Trowbridge 
as insufficient, on the grounds that they presuppose 
abnormal conditions in the case of Neptune, and do not 
account for the perpendicular rotation of Uranus, he points 
out that the different motions may be explained by the tidal 
action of the sun in the following manner :— 
Taking the case of Uranus as an example, let the line 
AB in the diagram represent the plane of the equator when 
this plane passes through the sun, let 
AC represent the plane of the planet’s 
orbit and imagine the planet beyond 
the sun. Then the point A on the 
equator of the planet would, in the 
rotation, travel in the direction AB. 
The sun’s attraction, in producing an 
annual tide, will produce a force AC 
acting on the particle A, with the con- 
sequence that A will travel along the 
resultant AD instead of along AB. 
This force AC will diminish during the 
planet’s revolution until, after a 
quarter of a revolution, it will be zero. 
After half a revolution, when the plane 
of rotation again passes through the sun, the senses of 
both AB and AC will be reversed, but the effect on the 
planet’s rotation will be the same as in the first case. This 
process will continue until ultimately the two planes will 
coincide when a direct rotation has been established. 
BRD 
Tue ‘‘ INVARIABLE PLANE’ OF THE PLANETARY SYSTEM.— 
In No. 3923 of the Astronomische Nachrichten, Prof. T. J. J. 
See publishes the results of a detailed discussion of the 
accuracy of the data now available for the determination 
of Laplace’s ‘‘ Invariable Plane ’’ of the planetary system. 
The elements of this plane are dependent upon the masses 
of the planets and the elements of their orbits, and the 
plane, when determined, would form a constant reference 
plane of great utility for the orbits of planets and comets. 
The transformations necessary to reduce star-places to this 
plane would be too cumbersome for practical utility. 
Prof. See, in the first place, explains the mathematical 
process by which the elements of the plane are obtained 
No. 1789, VOL. 69] 
NA TORE a5 
when the planetary data are known, and then gives the 
results previously obtained. In the second part of his paper 
he reviews and discusses the values hitherto obtained for 
the mass of each of the planets, and deduces that for the 
mass of Jupiter, which, owing to its relatively large magni- 
tude, acts as the most important factor of the reduction, 
the uncertainty does not amount to more than o ooo: of the 
whole. 
The elements obtained by Prof. See are as follows :— 
Ecliptic and mean 
equinox 1850 
Jan. o'0 G.M.T. 
where y=the inclination of the plane, and 2 =the longi- 
tude of its ascending node on the fixed ecliptic of 1850-0. 
In a subsequent table the author gives the longitudes of 
the ascending nodes and the inclinations of the planetary 
orbits on this ‘* Invariable Plane,’’ and, from a computation 
based on the relative positions of the planets at the epoch 
of 1850-0, he concludes that the actual shifting of the plane 
due to improvement in the data of the masses is not likely 
to exceed 1” for y and 1! for 8, a degree of accuracy 
approximating to that of our knowledge of the ecliptic and 
equator. He considers that a value for the inclination of 
which the probable error did not exceed +0"-20 would suffice 
for all practical considerations, and points out the import- 
ance of further work on the determination of the planetary 
masses, which only need to be a little more certain in order 
to produce this ideal result. 
Y=T° 35/774, 58 =106° 8’ 46-688 
SIMULTANEOUS SOLAR AND TERRESTRIAL 
CHANGES. 
HERE are very many cases recorded in the history of 
science in which we find that the most valuable and 
important applications have arisen from the study of the 
ideally useless. Long period weather forecasting, which 
at last seems to be coming into the region of practical 
politics as a result of the observation of solar changes, is 
another example of this sequence. 
The first indications of these changes on the sun, to which 
I have referred, are matters of very ancient history, and so 
also is the origin of some of the branches of observation on 
which the study of them depends. 
I will begin by referring to these and to the conclusions 
arrived at in relation to simultaneous solar and terrestrial 
changes previously to the last twenty-five years. 
The facts that there are sometimes spots on the sun, and 
that there is a magnetic force which acts upon a needle, 
seem to have been known to the ancient Chinese. In more 
modern times the inquiries, with which we are now con- 
cerned, date from the times of Galileo (1564-1642) and 
Kepler (1571-1630). 
To Galilec, Fabricius, and Scheiner we owe the first tele- 
scopic observations of the spots on the sun; to Kepler, the 
basis of spectrum analysis, which has not only revealed to 
us the chemistry of the sun and of its spots, but enables 
us to study daily other phenomena, the solar prominences, 
which will in all probability turn out to be more important 
for practical purposes than the spots themselves. 
It is only quite recently that the importance of the study 
of the prominences in this direction has been indicated, so 
that we have to deal, in the first instance, with a long period 
of years in which only the spots and their terrestrial echoes 
were in question. 
According to Prof. Wolf (as quoted by Prof. Koppen), 
Riccioli, in 1651, shortly after the first discovery of sun- 
spots, surmised that some coincidence might exist between 
them and terrestrial weather changes (Blanford, Bengal, 
Asiat. Soc. Journ., Ixv., part ii., 1875, p. 22). 
In the first year of the last century, Sir Wm. Herschel 
directed attention to this subject (Phil. Trans., 1801, p. 
265). He wrote :— 
“The first thing which appears from astronomical observ- 
ations of the sun is that the periods of the disappearance 
of spots on the sun are of much greater duration than those 
of their appearance. 
1 Paper presented to the International Meteorological Committee at 
SOE September 11, 1903. By Sir J. Norman Lockyer, K.C.B., 
