FOOT-WARMERS. 173 



Q. Why are HOT BKICKS (wrapped in cloth) 

 employed in cold weather to KEEP the FEET WARM ? 



A. Bricks are bad conductors of heat, 

 and cloth or flannel still worse : therefore 

 a hot brick (wrapped in flannel) will 

 retain its heat a very long time. 



Q. Why is a TIN PAN (filled with HOT WATER) 

 employed as a FOOT WARMER ? 



A. Because polished tin (being a bad 

 radiator of heat) keeps hot a very long 

 time ; and warms the feet resting upon 

 it. 



Q. What is meant by being a " bad RADIATOR 

 of heat ?" 



A. To radiate heat is to throw off 

 heat by rays, as the sun ; a polished tin 

 pan does not throw off the heat of boiling 

 water from its surface, but keeps it in. 



Q. Why is the TIN FOOT- WARMER covered with 



FLANNEL ? 



A. 1st To prevent the perspiration 

 of the foot from taking off the polish of 

 the tin : 



2ndly Flannel is a very bad con- 

 ductor ; and, therefore, helps to keep the 

 tin hot longer : and 



