Without time A With M 
Identity IN | Retroduction (symm.-moment). . . 
Inversion (centre). mel i Reversal-inversion,... << Gan «Dey 
Reflection (symmetry-plane) . sG 8 Reversal- reflection (reversal-plane) . MS 
Rotation (n-al axis) . RE a Reversal-rotation . . . .....MU 
Rotatory-reflection (n-al reflect.-axis) 2% Reversal-rotatory reflection. . . . MU 
Translation (place-period). Ak t Reversal-translation . . . . . . . ME 
Gliding-reflection (gliding plane). . 5 Reversal-gliding-reflection . ... MT 
Screw (n-al screw axis) „% Reversal screw .………. .…... ME 
With W With D 
Dilation (period). 0... p Reversal-dilation . . ......60O 
imiesinversion. …… ……. « c's S pi Reversal-time-inversion . . .. . D5 
Time-reflection (time-plane). . . . PS ps Reversal-time-reflection . . . . . D6 
Time-rotation . . .... . . . P% | pa | Reversal-time-rotation. . . . . . OU 
Time-rotatory-reflection. . . .. . PA Reversal-time-rotatory-reflection . . Hy 
Time-translation . .......WE Pt | Reversal-time-translation. . . . . OF 
Time-gliding-reflection. . .... ps Reversal-time-gliding-reflection. . . DF 
RE serewarn. Va rione hte vaya) Pee Reversal-time screw. . . .. . . Q& 
1427 
P and p. When an operation is combined with a reversal-dilation 
we add the prefix reversal-time and for the symbols 9 and q. 
Sometimes the name obtained in this way is still somewhat shortened. 
In the following table we find these provisionally fixed names 
together with the symbols. 
§ 11. The way in which s.-t.-symmetry-operations may be combined 
into groups. When the point groups of ScHoENriuEs are completed 
by those, which contain other than 2-, 3-, 4- and 6-al rotations ete. 
we can form from each of the thus found groups, s.-¢.-groups by 
combining each of the non-aequivalent operations of a group with 
either no time-operation or with a ® or witha, or witha 2. Each 
of the thus found groups must then still be examined to find out 
whether the time-operations added are perhaps in conflict with each 
other. Several of the groups obtained will also be found to be the same. 
The same might be done with the translation-groups.*), which are 
formed by ScHOENFLIES as a means to change point-groups into 
space-groups. After this, all obtained s.-é.-point-groups are multiplied 
by each of the s.-¢.-translation-groups found. Examples of such groups 
will be given in a following paper (N°. 76). 
1) In the case of translation-groups we have no longer a ground for the assump- 
tion that a and a © cause the paths to be closed. The only thing we should 
have won by omitting this hypothesis however would be the allowance of a conti- 
Ruous translatory motion of the whole system of particles. It would not be desirable 
to include this motion in our considerations. 
m 
mi 
ms 
ma 
mt 
qt 
qs 
qa 
qt 
