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THERE are two or three points in Dr. Pettigrew's new book as to which, perhaps, many of your readers in common with myself would be glad of a little light First, in speaking of the gannet, he says: â Each wing, when carefully measured and squared, gave an area of 19½ square inches.â But how is such an area obtained from the dimensions given ? They are : â girth of trunk, 18 inches,â i.e., about 5 inches for its width; â expanse of wing from tip to tip across the body, 5 feet,â so that each wing would stretch about 33½ inches from root to tip; â across secondaries, 7 inches,â and this we may take as about the average width of the wing. Multiplying length of wing by width (33½ à 7), we get therefore an area of 234½ square inches. Similarly Dr. Pettigrew assigns the heron's wing an area of 26 square inches, although the dimensions he gives yield an area of about 311 square inches. A friend of mine has the temerity to suggest 'hat for some reason or unreason Dr. Pettigrew has divided the true area by 12, for so 234½ (if we neglect the half inch) gives just 19½, and 312 instead of 311 gives 26. |
