722 
imperceptible; it amounts to 5 « 10~® times the force which the 
sun exercises on the earth. It deserves notice that this force is alto- 
gether independent of the assumed distance of the gas-cloud. It 
depends only on the amount of its absorption, and its apparent area 
in the sky. If this area is s square degrees, and the absorption « 
magnitudes, the formula of Rarrweicn gives, in the above manner: 
Force = 107 es X attraction of the sun on the earth. 
If the absorption is «' for photographic rays, (4 = 440) then « = '/, « 
is to be taken. If therefore in various directions and at various 
distances there are such absorbing gas-clouds in space round us, 
the total influence on our solar system can be calculated from their 
apparent area and absorption. 
For the time being we will consider only the influence proceeding 
from the Taurus gas-clouds. The perturbating forces are imperceptible 
also in the case of the most distant planets. But the force on the 
solar system as a whole is so immense, that (with a speed of 19 
km., supposed about perpendicular on the force), it must move in 
a curved orbit with a radius of curvature of 4 X 10° astronomical 
units = 2 parsecs, and the direction of the apex in 3000 years 
must be modified 1° towards Taurus. Compared with the distance 
of 140 parsees this slight radius of curvature indicates that our 
solar system must move in an elongated ellipse with excentricity 
°°/, around the gas-cloud; in a period of 2 a 3 million years, that 
at the present time it is nearly in the apocentre, and that in the 
pericentre it has practically to go through the gas-cloud. Something 
similar holds good for the Hyades, which run at a distance of about 
100 parsecs from the gas-cloud, with a speed of 45 km. To run 
away and get free from the nebula in a hyperbolic orbit, their 
speed would have to exceed 270 km.; with their small speed 
however they are bound soon to precipitate towards the gas-cloud. 
Such a huge mass as calculated above, would render it a central 
body dominating all movements in this part of the universe, over 
many hundreds of parsecs. The speed of the stars would be enormous 
in the vicinity of the gas cloud; especially in the direction of Taurus 
therefore, we should observe great proper motions, far exceeding 
the usual values. 
Also without the assumption of such a great attracting mass, the 
proper motions in the regions of absorption must be above the 
normal, because for a certain magnitude (on account of the dropping- 
off of stars behind the absorbing screen) the average distance there 
is smaller than elsewhere. Making use of the formulae of the previous 
