272 



THE BOTTOM OF THE SEA. 



the field of tlieir operations is necessarily limited — 

 an inconvenience which is remedied by moving the 

 bell laterally. In fact, tliis inconvenience is only 

 nominal when, as is often the case, the labour 

 consists in making an excavation in one particular 



Fig. 53. — Fixed Apparatus, supplied with Compressed Air. 



spot. In such cases the diving-bell may be even 

 advantageously replaced by apparatus employing 

 compressed air, and of such a form as the conditions 

 of the work demand. It was by the exercise of 



