55 



most efficient ventilation o£ tlie sewers, adopted in Adelaide as 

 its system o£ sewerage is being completed. We have the 

 advantage of knowing what has been done in England by the 

 best engineers ; we have the knowledge of the climatic changes 

 of the country, and we ought to have a drainage system based 

 it may be from English practical experience, but adapted to 

 our altered circumstances. 



I am indebted to our esteemed President for the comparison 

 of the climatic conditions of G-reenwich and Adelaide for the 

 year 1880 (vide appendix). I will quote the main points as 

 they bear upon our subject : — 



Geeenwich. Adelaide. 



The average mean temperature is 49 5 ... ... 63-3 



highest reading is ... 87'5 ... ... 114"5 



lowest reading is ... 17"2 ... ... 35'0 



mean daily range is ... 15'2 ... ... 18*9 



humidity is 83-0 ST'O 



rainfall is 29-68 22-47 



For ten months the mean temperature at G-reenwich is under 

 60°, whilst in Adelaide only during six months does the same 

 temperature prevail. For eight months the highest readings 

 at Greenwich vary from 61-4 to 87-5, whilst in Adelaide the 

 highest readings vary from 63-2 to 114-5. 



Barometric changes affect the amount of foul air present in 

 the sewers. The diminution in barometric pressure leads to 

 the escape of gases, which are stored in the interstices of the 

 sewage, and favours decomposition. An increase of barometric 

 pressure enables sewer air to carry a lar^rer amount of the 

 vapour of water, and for the sewage to retain a larger volume 

 of the offensive gases due to decomposition or absorption 

 without parting with them. Temperature and barometric 

 changes are therefore the fruitful agents by which air is 

 liberated from sewage, and it is consequently during atmos- 

 pheric changes that sewers which appear sweet at other times 

 become offensive and noxious. 



Under these conditions, and with the knowledge that in 

 England " preventible disease" caused by drainage is intimately 

 connected with temperature, and, as stated, usually commences 

 when the thermometer is persistently above 60°, inasmuch 

 as then the fa?cal emanations reach a certain rapidity of evolu- 

 tion in consequence of the high temperature, it behoves us to 

 examine these figures, which go to prove that in Adelaide the 

 decomposing matter will cause the sewer air to be in a constant 

 state of evolution, and, therefore, requires the most thorough 

 and perfect system of ventilation. I may here say that 

 extreme cold will prevent the germ matter from being diffused, 



