PAPERS ON CHEMISTRY AND PHYSICS 241 



furnaces and coal or oil water- and steam-heaters for 

 house heating ? 



2. How can an electric company supplying current to 

 consumers afford to maintain the pressure upon the pri- 

 maries of their transformers throughout the year, day 

 and night, when frequently, especially during the summer 

 months, little current is consumed? This condition is 

 true especially in villages and smaller cities. 



3. Why do shunt-wound motors, running without load, 

 or with light load, usually speed up tremenduously when 

 large resistance is placed in series with the field coils? 

 Why do such motors usually develop their greatest power 

 and efficiency, when moderately loaded, when a small 

 amount of resistance is still left in the field circuit 1 



4. In freezing ice cream why does the ice continue to 

 melt even when the temperature of the contents of the 

 freezer approaches zero Fahrenheit ? 



5. If an injured man is being carried up a steep hill 

 or up a flight of stairs upon a stretcher by two other men, 

 supposing that the center of gravity of the injured man 

 is at the center of the stretcher, midway between the sup- 

 porting hands of the bearers, is the weight of the burden 

 equally distributed between the two carriers, one of whom 

 is, perhaps, at an elevation of three or four feet above the 

 other? 



6. The vacuum cleaner demonstrator delights to show 

 the hesitating purchaser that even after a rug has been 

 thoroughly beaten on the grass or line the vacuum cleaner 

 TN-ill still remove much dust and diri from the rug. It 

 is equally true that the rug recei\'ing ordinary use and 

 being first cleaned by a vacuum cleaner and then hung 

 upon a line and beaten will still yield an ample amount of 

 dust and dirt. Why is this true ? 



7. Frequently the unqualified statement is found in 

 our physics textbooks that no machine can be so con- 

 structed as to yield 100% or more of efficiency when op- 

 erated doing work. Is this statement true ? If some em- 

 ployees are sent from a music store to remove a piano 

 from the fourth story of an apartment house and they 

 use a block and tackel to lower the piano from the fourth 

 story window, is the statement true? Is the statement 



