486 



SCIENCE 



[N. S. Vol. XXXIII. No. 



of arts, has heretofore been conferred upon 

 its graduates. 



At Smith College Harriet W. Bigelow has 

 been promoted to be professor of astronomy, 

 and Frances Grace Smith to be associate pro- 

 fessor of botany. 



At Yale University Dr. Alexander Petrunk- 

 evitch has been promoted to be assistant pro- 

 fessor of zoology, and Dr. Carl Johns, to be 

 assistant professor of chemistry. 



DISCUSSION AND COSBESFONDENCE 



THE AIE WE BREATHE 



To THE Editor of Science : As a member of 

 the American Society of Heating and Venti- 

 lating Engineers, who had the pleasure of 

 hearing the recent address of Dr. Gulick 

 before that society, I desire to reply to 

 his letter in Science of March 3. I believe 

 that Dr. Gulick is engaged in a research whose 

 results may be of the utmost importance to 

 the health of a large fraction of the human 

 race — namely, the children in the schools — - 

 and it is to be desired that he be given every 

 encouragement to continue in it. 



First, to answer some of his questions in 

 regard to the physics of atmospheric air. No 

 one knows " the reason why " raising the 

 temperature of air increases its capacity for 

 holding moisture. It is merely one of the 

 great facts of nature, like gravitation, and 

 like the fact that water freezes at 32° F. At 

 32° F. a cubic foot of air has the capacity of 

 holding in a gaseous condition 0.0003 pound of 

 water; at 62°, 0.00087 pound, at Y2°, 0.00121 

 pound, at 102°, 0.003 pound, and so on. 



" Is there any difference between steam and 

 humidity?" Steam is water in a gaseous 

 state. There is no difference between steam 

 and the gaseous or uncondensed vapor of 

 water in the atmosphere. When steam es- 

 capes from a pipe into an atmosphere colder 

 than itself it condenses into fog, which is vis- 

 ible, but if the atmosphere is not saturated 

 with moisture it will rapidly dry the fog, 

 turning it again into invisible vapor. Hu- 

 midity is the condition of the atmosphere as 

 regards moisture. Eelative humidity is the 



ratio or percentage that the moisture con- 

 tained in the atmosphere bears to the maxi- 

 mum quantity it can contain at the same 

 temperature. Thus if a cubic foot of air at 

 62° contains 0.00087 pound of water vapor, 

 the air is " saturated " and the relative hu- 

 midity is 100 per cent., but if the same quan- 

 tity of moisture is contained in a cubic foot of 

 air at 72° the relative humidity is only 

 0.00087 ~ 0.00121 or 72 per cent. 



" The manuals of the heating and venti- 

 lating engineers tell us that with a good sys- 

 tem of ventilation the opening of windows 

 causes only danger; yet as a matter of fact, 

 children in rooms so treated do not exhibit 

 the distressing conditions," etc. 



The " danger " from opening windows is not 

 to the children in the room in which the 

 windows are opened, but to the children 

 in the adjoining rooms in which the win- 

 dows are not opened. In the fan-blower or 

 " plenum " system of ventilation the entrance 

 and exit flues and dampers are so designed and 

 adjusted as to cause each room to receive its 

 due proportion of the total air supply. If a 

 window is opened in one room (unless the 

 wind is blowing towards the window) the re- 

 sistance to the passage of air from the room 

 will be less than if only the exit flue were 

 open ; consequently there will be a lower static 

 pressure in this room than in the other rooms, 

 and it will receive from the entrance flue more 

 than its proper share, thus robbing one or 

 more of the other rooms of their share. The 

 flow of air in a complex system of piping is 

 like the flow of water. If in an apartment 

 house with ordinary plumbing a tenant on a 

 lower floor draws hot water into a bath tub, 

 he will rob the bath room on the floor above 

 of its hot water supply for the time being. 

 So in a school-house fitted with air pipes, if 

 the flow of air from the fan into one room is 

 increased by opening a window, there will be 

 a smaller supply for the other rooms. The 

 " danger " therefore is that of unbalancing 

 the ventilating system. This danger would be 

 avoided if there were in use an automatic ar- 



