In the 17th century, Otto von Güricke, a

physicist in Magdeburg, fitted two hollow

bronze hemispheres together and removed the air from the resulting sphere with a pump. Two eight-horse teams could not pull the halves apart even though the hemi-spheres fell apart when air was readmitted. Suppose von Güricke had tied both teams of horses to one side and bolted the other side to a heavy tree trunk. In this case, the tension on the hemispheres would be

BLUE: twice

YELLOW: exactly the same as

PURPLE: half

what it was before.