This artist will appear at the Prism Coffeehouse tomorrow night, beginning at 10. He will perform material of his own composition as well as contemporary folk music, accompanying himself on twelve-string guitar. Jon Harris, formerly of the Slithy Toves, will play tonight at 9. Cover charge for both nights is $.50. The Prism is also planning another outdoor concert, tentatively April 27, featuring a broad spectrum of performers. Admission will be free but "the hat" will be passed with the proceeds going to the Transition fund. Anyone interested in working for the concert, performers or otherwise, are urged to contact any of the Coffeehouse management.