and Laboratory Methods 



2265 



Emphasis is also to be laid upon the protection of walls from exterior damp- 

 ness ; the defacement of walls, by the infiltration of water, adds to the expenses 

 of maintenance, not infrequently is injurious to exhibits, and complicates labor 

 by compelling the movement or reconstruction of wall cases. The air space in 

 the double wall, with both walls of the air cavity painted with tar, forms perhaps 

 the most complete defense against dampness. Such preservation in regions 

 visited by heavy storms, characterized by a wet climate, and exposed to oceanic 

 influences, is of very grave importance. 



Protection against dust merits serious consideration. The wood of sashes 



Fig. 2:5. — Vertical Section through Art Institute, Chicago. 



should be seasoned and past shrinkage, the runways of the window frames 

 should be deep, and the union of the double sashes in windows well secured by 

 two locks. Double windows can only be doubtfully recommended. Dust is a 

 variable accompaniment of position. It is more grievous naturally in dirty cities 

 than in clean ones, in tropical positions than in boreal, and on unpaved roads 

 and streets than where roads are properly paved, curbed and drained. The 

 prevalence of dust in the warmer seasons, when the windows of halls are 

 unavoidably open, can be sensibly diminished by keeping the neighboring streets 

 well sprinkled. And it will generally be found that proper representation, 



