2. A device as in claim 1 wherein said barometrically responsive retaining means comprises: band means wrapped at least once around said split link to retain said split link in integral condition; and a barometrically responsive release means connected to said band means.

3. A device as in claim 2 wherein: said split link has a detent on the exterior surface of each link to retain said band means.

4. A device as in claim 2 wherein: said band means is clamped at one end between said pieces of said split link and connected at the other end thereof to said barometrically responsive release means.

5. A device as in claim 4 wherein said barometrically responsive means further comprises: separable tongs which in their closed condition grip the other end of the band means; a spacer means to maintain said separating tongs in their closed condition; and pressure collapsible means connected to said spacer means so that when a preselected ambient pressure is reached the pressure collapsible means will collapse moving the spacer means and allowing the separable tongs to open thereby releasing the band means and freeing the first and second members.

6. A device as in claim 5 wherein: said pressure collapsible means is an evacuated bellows and a compression spring within said bellows.