674 
NATURE 
[| FEBRUARY 12, 1914 
Sweden. Of the American zones, one was observed 
at Albany, one at Washington, and two at Cambridge. 
Each of the latter occupied the time of an observer 
and several assistants for twenty years. It was ex- 
pected that these stars would be re-observed after an 
interval of about fifty years, to determine the proper 
motions, or annual changes in position. As the time 
is approaching when this great work should be under- 
taken, careful consideration should be given to it. 
Fortunately, the twentieth century has already 
developed two new methods, which might replace the 
older plans. The first of these is the transit micro- 
meter, in which a motion is given to the wire in the 
field of the telescope, so that it shall follow closely 
the motion of the image of a star as it transits through 
the field. A wide difference of opinion exists among 
leading astronomers as to the best method of securing 
this motion. In the earlier instruments constructed 
by Repsold, the motion was given by a screw turned 
by the two hands alternately. This method certainly 
gives excellent results, and is still used largely in 
geodetic work. Anyone who has tried it will find that 
with the rapid motion of an equatorial star under a 
high power, it is difficult to satisfy himself that the 
wire always bisects the star. If clockwork is used, 
the rate must vary with the declination, and it is 
strange that this is not done by electrical control 
instead of the somewhat crude mechanical devices 
now employed. The wire records its position auto- 
matically on a chronograph at short intervals. The 
plan of permitting this record only when the observer 
is satisfied that coincidence takes place, as is done 
at Heidelberg, seems a good one. Evidently a certain 
relative motion will give better results than a greater 
or less motion. It would appear to follow logically 
that this apparent motion should be given to all stars 
and the record permitted only for the few seconds of 
apparent coincidence. We can expect no better results 
than those obtained with a filar micrometer. The 
best plan may therefore prove to be to give a motion 
to the wire nearly equal to that of the star, whatever 
the declination of the latter, by a suitable variation 
of the clockwork. The best rate could readily be 
determined by observing stars at different distances 
from the pole. Successive settings should then be 
made as with a filar micrometer, closing the circuit 
on the chronograph only when the bisection was satis- 
factory. A similar setting should also be made for 
the declinations. The two coordinates could thus be 
determined with an accuracy substantially the same 
as that of a filar micrometer. Experience has shown 
that one star a minute can be observed in both co- 
ordinates with the transit micrometer. There can 
be little doubt that positions could thus be obtained 
with much greater accuracy than by the methods now 
in use. The special advantage would be the elimina- 
tion of systematic errors. 
A second method of determining positions, recently 
developed at the Allegheny Observatory, is by plates 
taken with a photographic doublet. Ordinary plates 
must be replaced by those of plate-glass. By taking 
suitable precautions positions may be determined of 
even the faintest stars, with an accuracy at least 
equal to that of a meridian circle. To obtain the best 
results, the field should be about 5° square on an 
8x10 plate. The focal length of the telescope would 
accordingly be about two metres. The large field 
would permit the constants of each plate to be derived 
from stars as bright as the eighth magnitude. The 
economy of this method would be very great, as com- 
pared with a meridian circle. The usefulness of the 
latter instrument appears to be confined to observa- 
tions of the brighter stars. ‘Accordingly, its aperture 
may be reduced. The ideal plan would apparently be 
NO. 23II, VOL. a21 
in fact, in almost every department of astronomy. 
to divide the sky into regions 5° square, and select in 
each five or more stars of about the eighth magnitude, 
and of approximately the same class of spectrum, as 
class K, so that all should haveabout the same colour. 
The positions of these should be determined with the 
greatest possible accuracy with meridian circles, as 
described above. Some brighter stars should be in- 
cluded to render available the vast number of observa- 
tions of these objects made in the past. Positions of 
the stars in the Gesellschaft catalogues and all fainter 
stars should be determined by photography. : 
Various attempts aré now being made to determine 
the absolute positions of the stars by means of photo- 
graphy. It appears probable that a pier placed under 
ground will remain free from irregular motions, and 
that if this can be accomplished, the absolute positions — 
of the stars near the equator can be found by photo- 
graphy. To determine the equinox, Venus and Mer- 
cury should be photographed, as well as the sun. By 
the very satisfactory cooperation of the Princeton, 
Yale, and Harvard Observatories, the position of the 
moon is now determined by photography. The results 
of a preliminary discussion indicate an accuracy at 
least equal to that of the best meridian determinations, 
those of the Greenwich Observatory. ha 
Excellent progress ic also being made in determin- 
ing the parallax of the stars by photography. The 
recent increase in accuracy is at least tenfold, or that 
of another place of decimals. A hundredth of a 
second of arc can be determined with greater accuracy 
than a tenth of a second twenty or thirty years ago. 
The just criticism has been made of American 
astronomers that while they have contributed more 
than their share of the work in astrophysics, the older 
science of astronomy of position has been greatly 
neglected. This is partly due to the fact that much 
of this work has been left to the United States Naval 
Observatory, which in the past has failed to justify 
the liberal appropriations made for its support. While 
Congress has given it for many years a much larger 
income than that of any other observatory in the 
world, the law has been such that it is impossible to 
attain the best results. The superintendent must be 
a naval officer, instead of an astronomer, and even 
then must go to sea after a short term. Accordingly 
the Naval Observatory during a period of thirty-seven 
years had twenty superintendents with an average 
term of fewer than two years. The Greenwich Ob- 
servatory during a period of 235 years, from 1675 to 
1910, has had eight Astronomers Royal, with an 
average term of twenty-nine years. The work of the 
latter institution with but half the income has greatl 
exceeded that of the Naval Observatory. It shoul 
be stated, however, that within the last few weeks 
the Naval Observatory has established an admirable 
wireless time service, by which anyone, at trifling 
expense, can obtain accurate time within a tenth of a 
second. The Navy has no need of a great observa- 
tory, from which it derives but little credit. 
sent unfortunate conditions, but the necessary action 
has not been taken by Congress. The obvious remedy 
is to remove the observatory to another department, 
or place it under the direction of the Smithsonian 
Institution, and appoint an astronomer at its head. 
What grander field of work could be undertaken by 
this observatory than that desired by astronomers and 
neglected elsewhere? For instance, computers of 
double-star orbits are continually complaining that 
while a surplus of measures of the easy objects are 
available, many difficult objects are 
although measures of them are greatly needed. The 
same is true of the asteroids, of variable stars, ard, 
Three | : 
successive Boards of Visitors have pointed out the pre- — 
neglected, — 
J 
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