Stir together. For an authentic shipboard Gimlet, do not add ice.
To make lime cordial, peel 4 limes, and juice 8 of them to make 1 cup of lime juice. Strain the juice and divide in half. Make a 2:1 simple syrup from half the lime juice, 1 tsp of citric acid and the peels, reducing the syrup slightly until thick. Remove from the heat, let cool, and add the remaining lime juice. Strain again and bottle. For a modern touch, a makrut (kaffir) lime leaf or two can be added to the syrup.
McElhone's book calls for equal parts, and I figure that this is a small drink.