| 摘要 |
<p>Photographic device for monitoring the condition of the inner wall of elongated cavities, in particular the filter tube walls of drinking water wells, in whose housing, which is kept relatively small, there is maintained a coherent film which enables many more pictures to be taken than in the past, so that even relatively long cavities of the abovementioned type can be photographed for monitoring purposes in one operation by a corresponding multiplicity of pictures, which are taken at relatively short intervals.</p> |
