Marine biologist and best-selling author of A Children's Guide To Blue Whales James W. Bradley has begun using the world's largest non-marine mammal, the elephant, as his standard unit of measurement not only in his work but in daily life as well, sources close to the scientist said Monday. 'From the 2.5- elephant weight of a city bus to the 12,204- elephant distance between Seattle and Tacoma, it's the only way he can visualize measurement anymore,' said his wife Celia Bradley, who is not a whale expert. 'We saw a rat in the street the other day and he kept going on and on about how huge it was, saying, 'That thing must've been at least .074 elephants long!'' Bradley was not available for comment, since he was reportedly closing on a three-bedroom, two-bathroom, 40-square-elephant house. 