PHENOMENA CONNECTED WITH CLOUDY CONDENSATION. 229 



It is tlionght that the Iconiscope will be useful for sanitary inspec- 

 tors for investigating' questions of ventilation in rooms lighted with gas 

 and for other pur[)oses. As an illustration of what this instrunient can 

 tell us, the following ex[>erinient may be given. It shows us how we 

 ean trace by means of it the pollution taking place in our rooms by 

 open tiauies. The room in wbich the tests were made is 24 x 17 x 13 

 feet. The object of the tests was to see if the Iconiscope could tell us 

 anything definite about the degree of pollution at the different parts of 

 the room, and also about the rate at wliieli it was increasing. Fortius 

 l)urpose a small tube was arranged so that one end of it could be raised 

 to the ceiling or into the air of any part of the room from which it was 

 desired to take the air; the other end of the tube was connected with 

 the yoniscope. 



The first thing to be done was to examine the air of the room before 

 lighting the gas and beginning the tests. On doing this the air at the 

 level of the observer gave a very faint color, scarcely perceptible; air 

 drawn froniAvitliin 3 inches of the ceiling gave equally little color, and 

 the air inside the room gave the same color as the air outside. The 

 ui)per end of the tube connected with the Iconiscope was then raised to 

 within 3 incliee of the ceiling, near one end of the room, and the koni- 

 scope left attached to the lower end. Three jets of gas were now lit in 

 the center of the room and observations at once begun with the l-oni- 

 Hcope. Within thirty-five seconds of striking the match to light the 

 gas the products of combustion had extended to the end of the room; 

 this was indicated by the color in the Iconiscope suddenly becoming of 

 a deep blue. In four minutes the deep blue producing air was got at 

 a distance of 2 feet from the ceiling. In ten minutes there was strong- 

 evidence of the pollution all through the room. It was strongly indi- 

 cated near the windows, owing to the down current of cold air on the 

 glass. Tills impure down current could be traced to the floor, and 

 onwards to the fire-place; while a pure current could be traced from the 

 floor to the lire-place. In thirty minutes the impurity at 9 feet from the 

 floor was very great, the color being a deep blue. 



The wide range of the indications of the Iconiscope^ from pure white 

 to nearly black-blue, makes the estimates of the impurity very easily 

 taken with it; and, as there are few parts to get out of ordei-, it is 

 hoped it may come into general use for sanitaxy work. 



The few experiments I have nmde with this instrument have clearly 

 ]»ointed out that a window is not an unalloyed blessing as regards the 

 purity of the air in our rooms, however much we may have been in the 

 habit of thinking otherwise. In all cases it has been found that in 

 rooms where gas is burning the air near the window is very impure. 

 This impure down current of air near the window has been traced by 

 the Iconiscope in all rooms tested. The impurity is caused by the cold 

 air on the window sinking and drawing down the impure air near the 

 ceiling, and this impure air is mixed with the lower air which we are 



