SECONDARY UNDULATIONS OF OCEANIC TIDES. 



Fis. 



is screwed into a lieavy lead disk D. By the tulie a, water 

 enters tlie vessel and compresses the enclosed air. The vessel 



A commnnicates with the recording- 

 apparatus by means of a brass tube 

 h and a long copper tubing / (in- 

 ternal diameter =2 mm.) ; the brass 

 tube is bent round as shown in 

 the above figure for convenience of 

 transportation. The recording ar- 

 rangement is almost the same as the 

 preceeding. In Fig. 4, B and C are 



two glass vessels communicating 

 with each other by a thick caout- 

 chouc tube, and partially filled 

 with mercury. The copper tub- 

 ing / from the diving jar is con- 

 nected to the glass vessel B. p 

 is the pen, gg the guiding pillars 

 for vertical motion of the pen, 

 and E the recording cylinder. If 

 the jar is placed on sea bottom, 

 the pressure of the enclosed air 

 is balanced by the pressure due 

 to the difference of tlie heights 

 of two mercury columns. The 

 change of pressure caused by the 

 change of sea level al)ove the 

 diving jar, forces the motion of 

 the mercury column in the vessel 

 C ; this motion is recorded by the 



Fig. 4. 



