86 GLASS SCREENS. 



and divide by nine, and substract 32 degrees from the quotient, 

 and vice versa when the opposite calculation is to be made. 

 Let me see if you understand it, by telling me what height 

 of Fahrenheit is equal to the 30 degrees of Reaumur of which 

 we were speaking. 



30 multiplied by 9, equals 270; divided by 4, equals 67; 

 add 32, equals 99^, the degree of Fahrenheit. 



V MRS. F. 



Very well; but now suppose it is below the zero of Reau- 

 mur, how would you then calculate it? We will say 40 

 below. 



ESTHER. 



We must then substract the 32, thus: 40 multiplied by 9, 

 equals 360; divided by 4, equals 90; subtract 32, equals 58 

 below the zero of Fahrenheit. 



MRS. F. 



Now convert 50 of Fahrenheit into Reaumur, and write it 

 down with the proper arithmetical signs. 



ESTHER. 



Here it is, mamma: 50 32=18x4=72-^-9=8, the de- 

 gree of Reaumur. 



MRS. F. 



I think now that you must all understand the difference 

 most clearly. I see, Mrs. Clifford, that you have one of the 

 new plate-glass screens; do you find it answer] 



MRS. c. 

 Most perfectly. 



HENRIETTA. 



I do not understand how a plate of glass should keep out 

 the heat of the fire; for when, in a sunny day, I sit in the 



