The Outdoor Girls at Rainbow Lake: Or, The Stirring Cruise of the Motor Boat Gem

From the book:"Girls, I've got the grandest surprise for you!" Betty Nelson crossed the velvety green lawn, and crowded into the hammock, slung between two apple trees, which were laden with green fruit. First she had motioned for Grace Ford to make room for her, and then sank beside her chum with a sigh of relief. "Oh, it was so warm walking over!" she breathed. "And I did come too fast, I guess." She fanned herself with a filmy handkerchief. "But the surprise?" Mollie Billette reminded Betty.