For our Wafer Supply, 



247 



and frosty nights, and I was anxious that the reservoir should 

 get every possible advantage. 



I must say, therefore, that I was greatly surprised to find 

 that Mr. Hodgkinson relied on ten inches of dew for the re- 

 servoir. 



I have looked in vain for any authority to bear out this 

 extraordinary opinion respecting dew, and I feel assured that 

 Mr. Hodgkinson could not have consulted the best authorities 

 on the subject. 



In England, from four to five inches of dew are supposed 

 to be condensed on the surface of the ground, and its produc- 

 tion is easily explained, and well understood. 



But Mr. Hodgkinson obtains ten inches for the reservoir^ 

 by assuming that this amount of dew is condensed on the 

 surface of water in this colony. 



This is a very important assumption, as ten inches in the 

 reservoir will supply 22,727, at forty gallons, per head, per 

 day, and 100,000 at nine gallons, which some allege is really 

 all that is required for ordinary consumption. At this rate 

 the dew condensed on the surface of the reservoir would 

 suffice to supply Melbourne, with all its suburban towns and 

 villages. 



Here, again, it is to be regretted that Mr. Hodgkinson 

 does not say upon whose authority he assumes this enormous 

 amount of dew. He certainly states that Mr. Thom, the 

 eminent practical engineer of the Paisley Water Works, and the 

 energetic promoter of the gravitation schemes of water supply 

 in Scotland, considers that the evaporation in large reservoirs 

 is counterbalanced by the condensation of dew, but this is 

 only to be regarded as his individual opinion, and is certainly 

 not based on accurate observation, or experiment. 



It is scarcely possible that Mr. Thom could have directed 

 much attention to the subject of dew at the time that he 

 uttered this opinion, and Mr. Hodgkinson himself shows that 

 Mr. Thom's statement is altogether inconsistant with the 

 production of salt by the evaporation of sea water, which has 

 been carried on for ages. 



Mr. Thom's opinions, therefore, on scientific subjects are 

 not very remarkable for their minute accuracy. 



Mr. Hodgkinson quotes his estimate of the available rain 

 on which he relies for the Paisley Water Works, which is 

 thirty-nine inches out of an annualrainfallof fifty-four inches. 

 I can readily understand how low swampy ground, that is 

 thoroughly intersected with catch-water drains, should yield 

 a much larger amount of water than the whole rainfall, because 



