Popular Science Monthly 



663 



Reverses Tug's Propeller- Blades 



WITH small boats, the quickest and 

 surest way to back-water is to 

 reverse the pitch of the propeller-blades. 

 Numerous motor-boats are equipped with 

 mechanism which performs the task by 

 the mere shifting of a lever, but in the 

 case of larger craft the blades 

 of the propeller are so heavy 

 that to reverse them by an 

 ordinary lever would be al- 

 most impossible. A large tug 

 that plies San Francisco Har- 

 bor was recently equipped 

 with a propeller -blade re- 

 versing mechanism, which, 

 while embodying the old lever 

 principle, accomplishes its 

 purpose in a surer and more 

 ingenious way. 



The blades are shifted by levers that 

 are controlled by a worm-gear, which is 

 in turn operated by a hand-wheel and 

 chain. When the wheel is spun, the 

 worm revolves, causing the levers to be 

 pushed in or out, the 

 pitch of the blades 

 being determined by 

 the direction and 

 number of turns of 

 the wheel. An addi- 

 tional advantage of 

 this type of blade 

 shifter is that the 

 pitch of the blades 

 can be altered, as de- 

 sired, to an almost 

 i n fini- 

 tesimal 

 degree. 



Fumigating Has Improved, But 

 Are We Less Afraid of Germs? 



IN these days of sanitary living, sani- 

 tary breathing, sanitary sleeping, san- 

 itary eating, etc., fumigation has come 

 to be one of the most popular of in- 

 door medical sports. Not a great many 



If the pitch of the propeller- 

 blades is reversed, the con- 

 tinued drive of the engine will 

 back the boat. Here is a device 

 which does just this thing with 

 complete mechanical success 



Cyanogen gas carried to your door — or 

 window — to fumigate your house 



years ago, when we 

 were still eating 

 butter that had not 

 previously gone un- 

 der the vigilant microscope of the 

 health officer, we considered that a little 

 block of sulphur burned in a room after 

 someone had had measles would annihil- 

 ate the last germ. Not long ago, how- 

 ever, an enterprising physician some- 

 where in the United States examined a 

 sample of wallpaper that had been on 

 the wall since a case of diphtheria had 

 run its course there a score of years be- 

 fore. On the sample he found an agile, 

 active colony of diphtheria germs. This 

 was not the sole cause, but it was one of 

 the immediate causes of wide-spread, 

 better fumigation. 



Cyanogen, deadliest of gases, is now 

 smoked into a room in which patients 

 having contagious diseases have lived. 

 The latest and one of the most effective 

 ways of dealing death to the lurking 

 microbe depends on a tank fastened to 

 the rear of an automobile. The automo- 

 bile is driven up alongside the house to be 

 fumigated, a hose is attached to the top 

 of the tank and led into the room. 



Structurally, the automobile fumigat- 

 ing machine is highly interesting. An 

 electric motor, attached to an air-pump, 

 is started in the bottom of the tank, 

 causing air to be forced through the 

 mixture of chemicals.' This air draft 

 carries the death-dealing gases through 

 the tube into the room. 



