THE MECHANICS OF VENTILATION. 473 



place throughout the whole atmosphere, iiot only out of doors but in as 

 great a degree inside. The atmosphere, considered as a whole, can never 

 be at rest, the slightest changes in temperature produce variations in vol- 

 ume, density and pressure, and these again are the causes of unending 

 motion. In short, we may say the air is perpetually in unstable equilibrium. 



The temperature at which inhabited spaces should be kept varies from 

 G0° to 65°, depending to a considerable extent upon the nature of the ope- 

 rations carried on. It is certain, moreover, that the temperature can be 

 kept lower without discomfort in well ventilated apartments, than in those 

 which are not well ventilated. Upon this point the writer has recentlj^ 

 made some investigations which may with propriety be introduced here. 



The revised charter of the city of Rochester, of last year, created a Board 

 of Health with more extended authority than that exercised by previous 

 boards. Among other items the new board has authority to regulate the 

 ventilation of public school houses throughout the city. During the past 

 winter the writer at the instance of said board made an extended examina- 

 tion of all the school buildings to the number of twentj^-five, and reported 

 thereon at length. In the course of the examination it appeared necessary 

 to ascertain exactly the temperature at which the several rooms were kept. 

 In going through them and using a thermometer in each it very soon be- 

 came apparent that there were extraordinary variations in the temperature. 

 The school-rooms, numbering more than 200, were then supplied with ther- 

 mometers, and the teachers carefully instructed as to the manner of taking 

 observations, &c. The observations were taken ten times a day for one week, 

 the times of taking being as follows : At the beginning of school, (9 a. m.); at 

 end of first hour, (10 a, m.); before morning intermission, (10.45 A. M.); after 

 morning intermission, (11 A. M.); at end of morning session, (12 M.); at be- 

 ginning of afternoon session, (1,30 p. m.); end first hour, (2.30 p. m.); before 

 intermission, (2.45 P. m.); after intermission, (3 p. m.); end of afternoon 

 session, (4 p. m.) 



These observations in connection with a careful consideration of the facil- 

 ities for ventilation furnished matter of the highest interest. They led, 

 indeed, to the inevitable conclusion that in school houses where the venti- 

 lation is thorough, pupils and teachers are perfectly comfortable at a 

 temperature of 60°-62°, and that the temperatures invariably increase as 

 perfection of ventilation decreases. So true is this that the following laws 

 are fairly deducible, which so far as an inquiry into the ventilation of school 

 houses is concerned, may be denominated the laws of temperatures. 



1. In rooms having but one outside exposure he temperature is uni- 

 formly higher than in those having two or more outside exposures, other 

 conditions being the same. 



2. Where the communication is direct by means of roomy halls between 

 lower and upper floors, the temperature ranges higher on upper floors, 



3. Of two rooms having equal exposure and equal heating and ventila- 

 ting facilities, the one containing the greater number of pupils will show 

 the higher average temperature. 



