Turning now to waters having considerable turbidities, at Pittsburg the average suspended matters in the Allegheny River water, as shown by the weekly or semi-weekly analyses of the Filtration Commission during 1897-8, were 4 parts in 100,000. During a large part of the time the suspended matters were so small that it was not deemed worth while to determine them, and the results are returned as zero. This is not quite correct, and a recomputation of the amount of suspended matters, based on the observed amounts, and the amounts calculated from the turbidities when they were very low, leads to an average of a little less than 5 parts in 100,000, which is probably more accurate than the direct average. The average turbidity on the platinum-wire scale was 0.16. At Cincinnati the suspended matters are about 23 parts in 100,000, and at Louisville about 35 parts, both of these figures being from Mr. Fuller’s reports. In all these cases the enormous and rapid fluctuations in the turbidity of the water is a most striking feature of the results. Observations on the Mississippi River above the Ohio have been made by Professor Long in 1888-9, and by Professor Palmer in 1896. These results are not as full and systematic as could be desired, but indicate averages of 20 to 30 parts in 100,000 at the different points. Professor William Ripley Nichols, in his work on water-supply, states the amount of suspended matter in the water of the Mississippi, probably referring to the lower river, as 66.66 parts. Investigations of Professor Long and Professor Palmer for numerous interior Illinois streams extending over considerable periods give average results ranging from 1 to 8 parts in 100,000. The very much lower results for the interior streams as compared with the Mississippi and Ohio rivers may be due to the relative sizes and lengths of the streams, or in part to other causes. Regarding muddy European rivers there are but few data. The Maas, used for the water-supply of Rotterdam, is reported by Professor Nichols as having from 1.40 to 47.61 and averaging 10 parts of suspended matters in 100,000. More recent information is to the effect that the raw water has at most 30 parts of suspended matters, and that that quantity is very seldom reached. At Bremen the Weser often becomes quite turbid. The turbidity of the water is noted every day by taking the depth at which a black line on a white surface can be seen. Assuming that this procedure is equivalent to the platinum-wire procedure, the depths at which the wire can be seen, namely, from 15 to 600 millimeters, correspond to turbidities of from 0.04 to 1.70, a result not very different from the conditions at Pittsburg.