Withy. — On Sanitation and Ventilation. 471 



the necessity of taking great care to prevent stoppages occurring 

 in any waste-pipes, and pointing out that periodical examination 

 and testing are most desirable. I should very gladly join an 

 association for the purpose of employing a competent expert 

 to «o round at stated intervals to see that the domestic 

 arrangements of its subscribers were in perfect order. We have 

 lately seen that Germany with all its immense expenditure 

 upon preparations to meet foreign foes and while proposing a 

 large increase of armaments was, in the bad sanitary con- 

 dition of two of its largest cities, courting the advance of 

 epidemic disease, and, as far as its hospital-accommodation 

 went, was totally unprepared to protect its citizens from the 

 foe after he had crossed the border. To be forewarned should 

 be to be forearmed. 



Lastly, no attempt to deal with sanitation would be com- 

 plete which omitted to deal with water-supply to our houses. 

 Whether this is obtained from public water-mains or is caught 

 in tanks from our roofs, every care should be taken to keep it 

 free from contamination of every sort, and even from the sus- 

 picion of it. If it is stored in tanks they should be cleaned 

 out periodically. In either case the water which is used for 

 ordinary drinking — i.e., such as will not be boiled — should be 

 passed through an efficient filter. The replenishing of this 

 should be the regular daily duty of some one in the household : 

 what is every one's duty is likely to be neglected. The filters 

 themselves require washing out occasionally by being laid 

 sideways and having water run through them in the opposite 

 direction for some time. 



Ventilation. 



I will commence this part of the paper, as I did that upon 

 sanitation, by considering the main facts affecting the move- 

 ments of the element which we have to deal with — viz., the air. 

 In sanitation we had to consider the action of two different 

 fluids — water and air — when passing through pipes ; in venti- 

 lation we have to consider the action of only one fluid — air- 

 when circulating through a house. The movements of the 

 atmosphere are caused by the heat of the sun, and the 

 familiar explanation of the cause of the trade-winds will serve 

 as a good illustration. When air is warmed it becomes lighter, 

 and consequently floats upwards. The greater heat of the 

 tropics causes the air in those latitudes to rise, and thereupon 

 the cooler air, for some distance northward and southward, 

 flows in to take its place. This process is continually going 

 on, and would result in a prevalence of northerly winds in the 

 Northern Hemisphere and southerly winds in the Southern 

 if it was not for another tendency produced by the revolu- 

 tio n of the earth upon its axis. The earth is continually 



