20 THE OCEAN 



a way that a jerk pulls out the stopper. In 

 deeper water a stopcock water-bottle was 

 employed during the " Challenger " Expedi- 

 tion for intermediate samples and a slip 

 water-bottle for bottom samples. 



Photometer. — For investigating the penetra- 

 tion of sunlight into the sea and the intensity 

 and composition of that light at different 

 depths, various forms of photometric appara- 

 tus have from time to time been employed. 

 The latest is that designed by B. Helland- 

 Hansen (see Plate I.) and used by him success- 

 fully during the recent cruise of the " Michael 

 Sars " in the North Atlantic. It consists of 

 a framework, on which two cubes, fitting 

 one inside the other, slide up and down, the 

 smaller cube having five openings, one on each 

 of the four sides and one on the top, for the 

 exposure of photographic plates with or 

 without colour filters. The cubes are carried 

 into the dark room, and the plates are placed 

 in the smaller cube, which is then enclosed 

 inside the larger cube and thus effectually 

 protected from the light. The two cubes are 

 suspended in the upper part of the frame, and 

 the apparatus is lowered to the desired 

 depth, when a messenger is sent down the 

 line to release the smaller cube, which falls 

 to the bottom of the frame, thus exposing the 

 plates. After the necessary interval a second 



