DEVELOPMENTS IN ASTRONOMY—PLASKETT, - 269 
roughly globular cluster about 15° in diameter. These stars are all 
moving with a velocity of about 40 kilometers (25 miles) per second 
toward a point in the northeastern part of Orion, about 35° from the 
center of the group. Their parallax, computed as before, is 0.025’’, 
or 130 light years distant. Boss has calculated that in 65,000,000 
years they will form a globular cluster about 21’ in diameter and of 
magnitudes 9 to 12. 
The most recent discoveries in star streams were given by Prof. 
Kapteyn, at the solar union meeting, on Mount Wilson, last August. 
He has found, by selecting from Boss’s Catalogue all the stars of the 
Orion type characterized by the appearance of helium lines in their 
spectrum and so called since most of the stars in the constellation of 
Orion are of this class, that in a large region of the sky they are 
moving in nearly the same direction and at nearly the same rate. 
This region contains the constellation Scorpio and Centaurus, cover- 
ing 4,500 square degrees and extending roughly from 12" to 18" R. A. 
to and from Dec. 0° to —60°. In another region of 1,300 square 
degrees in Perseus from 2° 50™ to 45 30™ R. A. and from +15° to 
+55° in Dec., all the stars of the same type are moving in a different 
direction. When motion of the sun among the stars is allowed for, 
Prof. Kapteyn finds that these apparent motions are equivalent to 
streams moving in exactly opposite directions and at equal rates. 
He finds these stars are very distant from the sun—from about 125 
to 500 light years. 
It is evident that the sidereal universe is a complex structure 
and having complex drifts and motions of stars and systems of stars 
in its part. We may be able to get a further idea of the magnitude 
of the problem by considering some of the recent results obtained 
for stellar distances. We all know, of course, that the nearest fixed 
star, a Centauri, is slightly over 4 light years distant, about 275,000 
times the distance of the earth from the sun, 25 millions of millions of 
miles. There has been a very marked advance in recent years in the 
determination of the distances of the stars, so that we now know with 
reasonable accuracy by direct methods the parallax or distance of 
about 200 stars. There are several indirect’ methods, one of which 
has been mentioned in connection with star streams, which give us 
what may be called mean or average parallaxes of groups of stars. 
I have not time to go into these methods, but it may suffice to give 
a couple of tables indicating in a general way the average distances 
of stars of different magnitudes and of different types. If we take 
the blue stars, those of the second magnitude are on the average 100; 
of the fourth, 200; of the sixth, 400; of the eighth, 800; of the tenth, 
1,600; and so on, light years away, doubling for a change of 2 mag- 
nitudes, while if we consider stars of different types we have from a 
