and sniid blnsting is highly irregulnr according to the profilometer trnces and the photomicrographs of Fig. 1. Horcver, if we mnke the nssumption that the p i n consists of n series of regulnr solid figures for this idenlised griiin
wliere Ii is n constnnt, the vnluc of which depends on the shape of the iilcnl iiidividunl cornpoiients of the p i n . Sererul of our results 1 2 3 I. nilo iloptli x lW, cm.
ha. R
have been plotted in this way (Fig. 3). The s l o p of the line is about 2/3 wliicli is wlint woultl be expected if the grnin consisted of a series of regulnr four-sided pyruniitls. The iiuniber of these pyramids per unit supcrficiiil iireir of specimeii ciin be conveiiictitly cnlled the grnin number niid ciin 1)c rendily cnlculirtcd. The griiin number shows some promise of bciug a quantity of importance iii the description of the gririns of lithogriipltic printing plntcs. The authors wisli to tlirink tlic Council of tlte Prititiiig niid Allied Trades Resenrcli Associntion for permissioii to publisli this paper. l'riiititig niid Allied Tritdes jteseiirch Associntion, Chitrterltouse Chtimbers, Cltrirterliouse Squnre, Lolldoll, E.C.l 1 J. d'A. Clnrk, h p o r Triidu Joiirnnl, 1942. 116 (I), 3% 2 6. A. Shuritlnn, Nittionnl I.ithogriqihur, l l M , 62 (7), 21. 3 P. 1' . Uowden nntl E. K. Ilitluiil, l'roc. Iloy. Soc.. 1028. A120, 81). 80. 4 F. 1'. Ilorvdun iind I<. A. O'Coiinor, I'roc. Iby. Soe., IUJO, AI28, 317. 6 e.y. ,!l. If. Grcsves tind H. \Yriglitoii, '' I'riicticsl Nicroscopicnl Motnllo. grapliy, Cliirpninu & Ha11 (I.ondun), 11. 14.