1 70 THE NEW WORLD OF SCIENCE 



are charged electrically, photographs of these oscillations show 

 simultaneously the behavior of a large number of particles, thus 

 simplifying the study of size distribution. For the more rapid 

 study of smokes an instrument called the Tyndall meter was 

 devised which measured the brightness of the Tyndall beam 

 set up in the smoke to be examined. For low concentrations 

 of smoke the brightness of the beam increases with the con- 

 centration and the degree of dispersity of the smoke material, 

 so that if either factor remains practically constant the readings 

 give a measure of the variation of the other. 



Using the Tyndall meter, the rate of disappearance of smoke 

 in a confined space was studied. The smoke gradually dis- 

 appears, owing to coagulation, to settling and to the diffusion of 

 the particles to the wall where they stick. The rate of dis- 

 appearance was markedly increased by stirring the smoke. 

 This rate increases with concentration of the smoke, owing to 

 the increased chance for coagulation and removal by the walls. 

 It is also greater for a finely divided smoke of a given concen- 

 tration than for a coarser smoke owing to the increased oppor- 

 tunity for coalescence. 



Several forms of smoke producers were developed for the 

 navy as a protection against submarines. The Navy Smoke 

 Funnel consists of a large horizontal cylinder approximately 

 two feet in diameter and 10 feet long with a hand operated 

 blast fan at one end to drive air through the funnel. The 

 apparatus is placed on the deck of a vessel and if a submarine 

 is sighted a dense smoke cloud of tremendous volume is pro- 

 duced for a period of thirty minutes. The Navy Smoke Box 

 consists of a metal container 8" in diameter by about 26" in 

 height, holding 100 Ibs. of the Bureau of Mines Smoke Mixture. 

 Attached to the cylinder are a float and a starting mechanism. 

 When ignited and thrown overboard, this smoke box evolves a 

 dense smoke for 9-12 minutes. An excellent smoke can also 

 be obtained by spraying sixty per cent, oleum into the smoke 

 stack of a ship. One drum of oleum (800 Ibs.) will produce 

 a smoke cloud of very large volume for one hour. The smoke 



