Bikini in the Regency? Not so much. But you can see her ankles. This is what you wore on the beach two hundred years ago. Mind you I have spent some chilly days on an English beach in July as a kid, as well as some lovely warm ones.
WALKING DRESS - from Ackermann's Repository for July 1815
A HIGH dress, of short walking length, made of French cambric or jaconot muslin, trimmed at the feet with treble flounces of French work, gathered into a rich bead-heading, and laid upon the dress, at a suitable distance, one above the other;
the body made with open fronts, worn with a full ruff of the French work, corresponding to the trimming at the feet; a long sleeve, drawn alternately across the arm, terminates with a broad wristband, worn plain over the hand.
French bonnet of white satin, edged and tied under the chin with satin ribbon of celestial blue; ornamented with a rich plume of white feathers, edged to correspond.
French mangle of the twilled silk en suite, richly embroidered at the ends in shaded silks, composing roses or lilies of the valley. Patent silk stockings. Slippers, or half-boots, of blue kid, or primrose colour. Gloves to correspond.
Additional note regarding general fashions for the month
The bodies of the morning and promenade costume continue to be worn with cross or handkerchief fronts, and are generally trimmed, agreeably to the texture of the dress, with quilled tull or ribbon. The quilled ribbon is also predominate in single rows at the feet of all dresses composed of silk, bombazeen, or fancy prints. The prevailing colours are primrose, celestial blue, and evening primrose; the waist short, and the fullness of the petticoat carried to the back. Ruffs of French work are universally worn, except in full dress. The length of the petticoat continues not to exceed meeting the top of the boot; and the colour of the latter corresponds with the glove, mantle, and trimming of the bonnet.
I love the sound of celestial blue, don't you? Until next time.....