資料來源 : Webster's Revised Unabridged Dictionary (1913)

TABLE OF THE PERIODIC LAW OF THE CHEMICAL ELEMENTS (The vertical
columns contain the periodic groups) Series1[ 2[ 3[ 4[ 5[ 6[ 7[
8[ 9[ 10[ 11[ 12[
--------------------------------------------------------------
|I. II. III. IV. V. VI. VII. VIII. | RH4 RH3 RH3 RH |R2O RO R3O3
RO2 R2O5 RO3 R2O7 RO4
-------------------------------------------------------------- H
1 Li 7 Na 23 K 39 (Cu) 63 Rb 85.2 (Ag) (108) Cs 133 (-) (-) (Au)
(197) (-)

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   Note: A similar relation had been enunciated in a crude way
         by Newlands; but the law in its effective form was
         developed and elaborated by Mendelejeff, whence it is
         sometimes called {Mendelejeff's law}. Important
         extensions of it were also made by L. Meyer. By this
         means Mendelejeff predicted with remarkable accuracy
         the hypothetical elements ekaboron, ekaluminium, and
         ekasilicon, afterwards discovered and named
         respectively scandium, gallium, and germanium.

   {Periodic star} (Astron.), a variable star whose changes of
      brightness recur at fixed periods.

   {Periodic time of a heavenly body} (Astron.), the time of a
      complete revolution of the body about the sun, or of a
      satellite about its primary.