JOHN THOMAS AND LADY JANE
by D.H. LAWRENCE 372 pages. Viking. $8.95.
THE TORRENTS OF SPRING by ERNEST HEMINGWAY 90 pages. Scribners. $5.95.
Permanent as the printed page may seem, the life of a book is often precarious. Nothing is harder to find than last year's literary flop, and the classics of yesterday seem to drop from view with unsettling regularity. The bottoms of the Great Lakes are said by some to be tiled with the dumped overstock of paperbacks that cannot be obtained anywhere, even in libraries. But there are mysterious cycles of...