Figurę 1Ł8. In (a) *. = O for 4G. We can change *, in iwo w*ys: (b) if wetihlhe ipf n— Uwoogh sagłe t\, ihc row cf spon -w iiaidc rhc sph«c; (c) if wc liłc ihc beara ihrotigh abovc Ihc spccimcn. in ihe oppo-site dffcoion, the sphcrc raoves ouiside the row of spots.