Many American families once had stereoscopes in their parlors, where they amused themselves on long winter days by looking at eye-popping, 3-D images of places they hoped to visit, including Florida. Shivering in northern cities in January, they could imagine being surrounded by steamboats and citrus groves, silvery lakes and sandy city streets. Postcards, too, spread images of Florida far and wide. If they didn’t have the snap of 3-D, the scribbled text messages they carried offer fascinations for present-day collectors.