On the Construction of Dams, dec. 257 



than lias yet been registered in any year since the establish- 

 ment of the Observatory in 1840. It has entirely con- 

 tradicted the assumption (which the observations of previous 

 years had warranted) of the alternation of wet and dry 

 seasons. The months of May, July, and November were 

 particularly distinguished ; and in the latter month alone 

 there were 9 inches of rain — a very unusual monthly 

 quantity for this climate. The mean temperature of 

 November is below the average, owing to the constant w^et, 

 cold weather : and at Midsummer — viz., on the 23rd of 

 December — Mount Wellington was completely covered with 

 snow, extending down to the low hills in its vicinity. The 

 weather during the night of the 22nd of December, and 

 morning of the 23rd, was as severe and inclement as during 

 any day in Mid-winter. 



XXIII. 



On the Construction of Dams, toith a View to Irrigation, 

 By Sir W. T. Denison, F.K.S., dec. [Bead Wtli 

 December, 1850.] 



As the subject of Irrigation is one of much importance to 

 the interests of the agriculturists and flockowners of this 

 colony, any information connected with the subject, or with 

 the mode in which it may best be carried out, will be useful. 

 I have therefore thought that a paper on the construction of 

 Dams, which was contributed by me in the "Aide Memoire" 

 of the Corps of Eoyal Engineers, and which treats of the 

 modes of constructing such works in a rapid, yet substantial 

 manner, of materials easily procured, would not be unac- 

 ceptable to the Koyal Society. 



