354 



H. M. Vernon 



of 16 cm. with the Saud under examination, and a stream of water 

 allowed to flow in from above. The sieve and dish over the tubulure 

 entirely prevented any sand from being carried away by the curreut 

 of water. The depth of water wheu the bell-jar was full was 12 cm. 

 The diameter of the jar was 15 cm., thus giving* a superficial area 

 of about 177 sq. cm. of sand. Through this apparatus, and another 

 of exactly similar construction, currents of water were allowed to 

 flow continuously for several weeks, the entering- and outflowing water 

 being analysed from time to time. The following results were 

 obtained for filtration through fine saud, which had been kept 

 stagnating in a small tank in the Aquarium for some weeks, and 

 which was impregnated with but small quantities of diatoms and 

 sdgsb. 



