Wash tangerines well and grate the peel in fine shreds into a bowl. Juice the tangerines and strain 2/3 c of juice into the same bowl, saving any extra juice. Put the cold water in a small pan and sprinkle the gelatin into it. Beat the eggs with the sugar until they hold a slight peak. Whip the cream until it forms soft peaks. Dissolve the gelatin over low heat. Slowly add the juice & peel mixture to the gelatin, stirring constantly. Fold the whipped cream into the egg and sugar mixture. Pour the gelatin-juice mixture into the cream mixture, whisking briskly where the juice goes in to keep it from jelling before it is thoroughly mixed. It will tend to jell and make little lumps otherwise. Taste and add some of the reserved juice or a little lemon juice if you would like more tartness or a stronger flavor. Chill for several hours or overnight, whisking occasionally during the first hour to prevent it from separating. Serve in a glass, garnished with a few shreds of tangerine peel, accompanied by Lace Cookies (dipped in chocolate if desired) or Langues de Chat.