1895.] Conditions affecting Bacterial Life in Thames Water. 439 



by the electrometer. We then tried 24, 48, 72, 96, 120 wire-gauze 

 discs, successively, placed in groups of 24, and separated from one 

 another by short lengths of 2 cm. of lead tube, in the line of the flow of 

 the air between F and G (fig. 1), all kept in metallic connection with 

 the block-tin pipe and the outer case of the electrometer. We were 

 surprised with the smallness of the additions to the diselectrifying 

 efficiency of the 12 strainers first tried ; for example, the filter of 120 

 wire gauzes only reduced the electrical indication to a little less than 

 one-half of what it was with the 12 which we first tried. 



We found that cotton- wool between the spaces in the groups of 

 24 wire gauzes largely increased the diselectrifying effect. Thus, 

 with 72 wire gauzes and cotton-wool we succeeded in reducing the 

 electrical effect to about one-twelfth of what it was with only a filter 

 of 12 wire gauzes ; but hitherto we have not succeeded in rendering 

 imperceptibly small the electricity yielded by the outflowing air to 

 the testing filter B in our method of observation. 



6. We intend trying various methods of obtaining more and more 

 nearly complete diselectrification of the electrified air flowing out of 

 the can at F ; and this for air electrified otherwise than by the needle 

 point, as shown in the diagram : for instance, by an electrified flame 

 in place of the needle point ; or again by bubbling through water or 

 other liquids. Meantime, the mere fact that the electricity, whether 

 positive or negative, given to air by an electrified needle point, can be 

 conveyed through 3 or 4 metres of small metal tube (1 cm. diameter), 

 and shown on a quadrant electrometer by a receiving filter, is not with- 

 out interest. We may add now that, with the receiving filter removed 

 and merely a fine platinum wire put in the mouth of the paraffin 

 tunnel, we have found that enough of electricity is taken from the 

 outflowing air to be amply shown by the quadrant electrometer ; 

 which renders even more surprising the fact that the diselectrifying 

 power of 120 strainers of fine wire-ga-uze should be so small as we 

 have found it. 



II. "On the Conditions affecting Bacterial Life in Thames 

 Water." By E. FRANKLAND, D.C.L., F.R.S. Received 

 January 31, 1895. 



Since May, 1892, I have been making monthly determinations of 

 the number of bacteria capable of development on a peptone-gelatine 

 plate in a given volume of Thames water collected at the intakes of 

 the Metropolitan water companies at Hampton. The number of 

 microbes per cubic centimetre of water varied during this time 

 between 631 and 56,630, the highest numbers having, as a rule, been 



