DR. REDMAYN&S APPARATUS. 



139 



press the tube firmly against the stick at c and the bottle be 

 lowered until the mouth of the tube is within a quarter of 

 an inch of the diatoms ; the thumb is then to be raised, and 

 if the water is deep the bottle will fill by atmospheric pres- 

 sure, carrying in the diatoms at the same time. In shallow 

 water suction will be necessary to exhaust the air in the 

 bottle, in which case the bulb pipette shown at B in the 

 same figure will be useful as a mouthpiece. 



In the collection and recognition of 

 diatoms, the student will find Professor 

 Brown's pocket microscope a useful ad- 

 junct, as it is furnished with a deep 

 eye-piece and objectives of an inch, and 

 a fifth of an inch focus. It is shown in 

 Fig. 123. 



Great care should be taken in the 

 collection of diatoms, so as to have them 

 in as pure a state as possible, as it is 

 not easy to separate them from foreign 

 matter when it is mixed up with them. 

 The late Dr. Redmayne placed the 

 gathering in a long bottle in the sun for 

 a few hours, the lower half of the bottle 

 being covered with black paper. The 

 free diatoms separate themselves from 

 the mud and come to the surface, and 

 can thus be removed. 



Fossil Diatomaceae also exist in im- 

 mense quantities in various places. The large deposits of 

 guano, the Bermuda deposits, the Berg-mehl in Norway, 

 the Mourne Mountain deposit in Ireland, the recent dis- 

 covery of diatoms in the London clay by Mr. Shrubsole, 

 and the still more recent discovery in Llyn Arenig Bach, 

 about midway between Bala and Festiniog, in North Wales, 



FIG. 123. 



