SABINE. — ARCHITECTURAL ACOUSTICS. 



69 



The next experiment, taking them up chronologically, and perhaps 

 next even from the standpoint of interest, was in regard to a brick 



.10 



.09 



.08 



.07 



.06 



.06 



.04 



.03 



.02 



.01 



I ^-^-^ ^^ 



Cx 



c. 



c, 



a 



c. 



Figure 4. 



Tlie absorbin{r power of a 45 cm. tliick brick wall. The upper curve represents 

 the absorbing power of an unpainted brick surface. The bricks were hard but 

 not glazed, and were set in cement. The lower curve represents the absorbing 

 power of the same surface painted with two coats of oil paint. The difference 

 between the two curves represents the absorption due to the porosity of the bricks. 

 In small part, but probably only in small part, the difference is due to difference in 

 superficial smoothness. C3 (middle C) 256. 



wall surface. This experiment was carried out in the constant tem- 

 perature room mentioned in the previous papers. The arrangement 

 of apparatus is shown in Figure 3, where the air reservoir in the room 



