THE TOURIST IN YOSEMITE, 1855-1985 by Stanford E. Demars (University of Utah: $19.95; 168 pp.). It's surprising, at least to the modern reader, to learn that Yosemite has been valued during the last century primarily for being "useful." Almost everyone who visited Yosemite (with major exceptions such as John Muir) sought aesthetic stimulation, spiritual elevation, exercise, physical thrills or stories to tell the folks back home; few thought to appreciate the place simply for itself. Stanford Demars, a professor of geography at Rhode Island College, lays out the changing attitudes toward Yosemite in a workmanlike manner, but the material suffers from his attempt to be supremely evenhanded. Demars justifies the valley's commercial development as keeping it safe from timber, mining and water interests, but that development also has led to the arrival of more than 3 million visitors annually, ensuring that virtually no one today can achieve the "Yosemite experience" that once made the place special.