| 摘要 |
A thermally insulating transparent wall element comprises a plurality of paraxially, adjacently arranged evacuated transparent tubes each having an axially arranged shaft journalled therewithin, an elongate sunshade strip being mounted on each shaft. A ratchet wheel is supported on one end of each shaft and has at its circumference engaging elements situated at the same angular distance from one another. An externally operable pawl cooperates with the engaging elements of the ratchet wheel to advance the same in step-wise manner. Means is provided to drive the pawl; and a member is coupled to the pawl drive means for latching the ratchet wheel at the end of each movement step, such member being releasable from the ratchet wheel by the pawl drive means just before the start of the next movement step.
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