45, COBNHILL, B.C., AND 122, KEGENT STREET, W., LONDON. 51 



FIG. 61. 



71. Portable Patent Maximum and Minimum Registering Thermo- 

 meters. Negretti and Zambra's Small Patent Maximum and Minimum 

 Registering Pocket Thermometers, fitted into a secure and convenient 

 pocket case, special for travellers, (fig. 61.) Price . . . .220 



Larger Standard size ditto 2 10 



The construction and use of the Portable Registering Thermometers is 

 identical with N. and Z.'s larger Standard instruments, Nos. 40 and 53. These 

 are the only Registering Thermometers that will travel without dera-ngement. 

 Explicit printed instructions for use accompany each set. 



72. Marie Davy's Actinometer, consisting of two Thermometers 

 in vacuo, one with a bright and the other with a black bulb, both divided on the 

 stems and mounted upon a suitable stand for out-door exposure. Price, 330 



RULES FOB CONVERTING THERMOMETER READINGS. . 

 To convert Fahrenheit readings to Centigrade. 



Subtract 32 and multiply the remainder by - 



y 



e.g. 68 P.=( 68 32)x- = 20 C. 

 y 



To convert Fahrenheit readings to Reaumur. 



Subtract, 32 and multiply the remainder by - 



e.g. 68 F.=( 68 32) X - = 16 R. 



To convert Centigrade readings to Fahrenheit. 



Multiply by f and add 32. 

 o 



To convert Reaumur degrees to Fahrenheit. 

 Multiply by | and add 32. 



To convert Centigrade to Reaumur. 



Multiply by - 

 5 



To convert Reaumur to Centigrade. 

 Multiply by | 



NOTE. All of Negretti and Zambra's Standard Thermometers may be had with. 

 Centigrade or Reaumur Scales to order. 



E2 



