in Melbourne. 201 



and that the difficulty of removing them increases with 

 delay so rapidly, that there is risk of its becoming one day 

 insurmountable if now neglected. The frequent use of the 

 first person was difficult to avoid under the circumstances — 

 it is not egoism. 



I^ote. — I avail myself of the scanty leisure which I have 

 had since the adjournment of this paper, to offer some 

 additional notes. 



Some of our writers have anticipated and misunderstood 

 the object of the paper, and have supposed from the fact 

 that the water has lately been in bad order, that it was 

 going to be denounced as containing a direful amount of 

 filth. For some time past the water of the Yan Yean has 

 been a high and certainly not attractive colour, and has 

 been more or less turbid. This condition has no necessary 

 connection with the question .above discussed. It was 

 observable when the supply was newly opened, and from 

 very similar causes. We have had a season of drought, the 

 contents of the reservoir were reduced far below the mean 

 level, and subsequent heavy rains have stirred up the bottom, 

 and diffused flocculent debris through the whole bulk of 

 the liquid, which debris being only slightly heavier than the 

 water does not quickly subside. Moreover, the floods carried 

 with them into the reservoir a large amount of peaty matter in 

 solution, as well as other substances in suspension. But 

 during the past month's comparative quiescence the water 

 has regained much of its original character ; its colour is 

 now much better ; it cleans itself much more rapidly ; and 

 the spontaneous precipitate is not only much smaller, but 

 is recovering its colour, the healthy green tint before alluded 

 to being now noticeable. I hope to illustrate this part of 

 the subject on a future occasion. The minute vegetal 

 organisms (Desmidias) are illustrated by the photograph, 

 fig. 5. 



I regret to have seen advertisements setting forth as 

 recommendatory of certain filters that the Yan Yean con- 

 tained some objectionable substances mentioned by name, 

 and that the filters in question, and those only, would 

 remove them. I know nothing of the firm so advertising, and 

 am quite willing to assume that its filters are very good, but 

 I deem it right in the public interest to declare that the nox- 

 ious substances mentioned do not and never did exist in the 

 water, and that if they did exist, no filter would remove 

 them. It is not the function of a filter to remove matters 



