182 Probable Influence of Evaporation on the 



In investigating the probable supply of water derivable 

 from the mountains, the possibility of any of the copious 

 streams in the ravines of Mount Disappointment being 

 derived from sources beyond the apparent limits of the water- 

 shed of the Plenty must next be considered. 



"When I guaged these streams and examined their sources 

 in 1852, the fine body of water that I saw gushing out with 

 great velocity from a fissure in the granite, and forming the 

 source of the Saw Pit Creek, on the western branch of the 

 Plenty led me to investigate this point ; as I was aware, 

 that in'the island of Hong Kong, copious streams gush out 

 of similar fissures in the granite formation there, and dis- 

 charge a much greater quantity of water than the total rain- 

 fall of the island. i ^ xi. 



But on examining the sources of the eastern branch ot the 

 Plenty, I saw that the high table land forming the dividing 

 ran"-e between the Plenty and the tributaries of the Lroul- 



and Water Supply has published a vindication of the Yan Yean Scheme of 

 Water Supply- the course of his observations, he states that I have com- 

 « Z n.ible error in io-norins?, in the above analogical deduction, the dif- 

 SencetnSith 0^^ days here lind in England, for the months of corre- 

 sZdTnl mean temperature; as he is of opinion that the evaporation, on 

 accou^rf longer dvfration of daylight, is greater in England, during a month 

 of Hertam mean temperature, than would he found to occur here, during a 

 month poSessin.. the same mean temperature. But Mr. Griffiths, m the calcu- 

 at^ bTS he iUustrates his views on this subject, unfortunately Mis into 

 the e^-ror of supposing that evaporation invariahly ceases at mgUfall. I, there- 

 fore be<^ to remark, that in this Colony, where dry windy nights are of such 

 frimient occurrence the nocturnal evaporation is often very great; so much so, 

 fn fact as to i^^^^^^^^^ correction, to which Mr. Griffiths attaches so much im- 

 portance of a very trivial and indefinite nature; no , however, ignored by mc, 

 V! rnnocps but found to be more than counterbalanced by the greater dry- 

 nL^ of tT2iShS this Colony. Mr. Griffithsfurther states,_that 1 arn 

 ness 01 tne "obp , tanneries, fellmongeries, and the 



thoUnd :th J r/y in?eaing Uces of pollution," to. the Plenty The 

 thousana owier ^ J ^ ^ j proposed to derive any supply, was 



^.„...^^c.»«^ to Md^^^^^^^ the point where the analytical chemist of 



two mdes ^S^%^P,™c river v ^ ^^^^^ ^^^^ 



the CommisWo^d the Ya™ ^arra, below f)ight's Mills 



See Ling o"ce Btaied the necessity, in my humble opinion, (in a casua 

 Lnver^atirSi Mr. Griffiths, two yeaxs ago,) of some legislative enactment 



IXrieSedlro^n Esq., Engineer to the Pitz- 



I have also lately "^ecewctt iron conveying to me the result of his ob- 



o\X pCty ' ^KaSn"^^^^^^ professional standing and long 

 servationson the Plen^^^^^^ his opinions on the Water 



six on^<reS^^ i«i>§--«^ flo- of the eastern arm of the Plenty 



feupply. -H-e coubiut s convinced, from long personal observation of 



llfvan^Y r ^^■Zr^.:t^<^^o:^on from thf sLface of the reservoir 

 tmle verrmuch lesf than has been estimated by some of the members of this 

 Society. 



