142 



Failure of the Yait Yean Reservoir, 



to clieck this result, they consult Mr. Dempsey's tables, and 

 find that exactly 5V"6 per cent, of the rain in England is 

 evaporated, and 42*4 per cent, goes to the rivers; and, for- 

 getting that this coh)ny is not England, and that our 

 tein])erature is much higher, and that the evaporation from 

 the surface of our imcultlvated lands is vastly greater, they 

 regard this coincidence as a jn^oof of the correctness of their 

 theory, and forthwith apply Mr. Dempsey's English evapora- 

 tion to determine the discharge of the Plenty river in the 

 Avinter months. 



This extraordinary coincidence between their calculations 

 and Mr. Dempsey's tables, even to a decimal fraction, might 

 at first sight, be supposed to prove the mathematical accuracy 

 of both, but a mere coincidence is not to be regarded as a 

 proof of the correctness of either, it is necessary that one or 

 other should first be established on a firm scientific basis before 

 such a coincidence could prove anything at all. I shall not 

 attempt to explain this singular coincidence, though, doubtless, 

 it would form an interesting sid)ject in an essay on probabilities. 



I have already shown that Mr, Dempsey's tables give three 

 times the amoTUit of watershed that Dr. Thomson calculated 

 for Great Ih'itain, and I am prepared to show that they give 

 a very erroneous and incorrect result of the proportion of the 

 rain that is evaporated here, for, when corrected for the 

 difference of temperature, they give only one-fourth of tlie 

 watershed calculated by the Committee, and therefore the 

 data upon whicli they rely to check their own calculations 

 will prove tliat they are altogether unworthy of confidence, 

 and must be divided by four to give a truthful result. 



It appears, from the report, that the Connnittee chiefly 

 rely on the eastern arm of the Plenty, for the supply of the 

 reservoir. 



Taking their own measurements in January, as the summer 

 discharge, although, in consequence of rain, it considerably 

 exceeded Mr. Blackburn's measurement in December, with a 

 velocity of one and one-third mile per hour, it only gives 

 4,450 gallons per minute, which for the six summer months 

 is equal to three feet in the reservoir ; their Avhole discharge 

 for the Plenty they calculate at twenty-four feet eight inches 

 in the reservoir, therefore the winter discharge for six months 

 Avill be eight times the amount of the summer discharge ; but 

 the section of the river will only contain three times the 

 volume, supposing the stream to be level with the banks, with 

 the same velocity, and they do not calculate for an increased 



