45, COKNHILL, E.G., AND 122, BEGENT STREET, W., LONDON. 



33 



FIG. 34. 



30- 



70- 



30- 



40 



FIG. 35. 



into a reservoir of mercury, and the whole hermetically sealed, as in our 

 Standard Deep-sea Thermometers ; by these means the bulb is effectually 

 protected from the pressure of the atmosphere, either from barometrical 

 changes or difference in altitude, and the divisions on the stem are so covered 

 by the outer glass tube that they cannot be effaced or become invisible. [ 



40. Board of Trade Thermometer. It consists of a carefully compared 

 thermometer with ISTegretti and Zambra's enamelled tube divided on its stem to 

 degrees, which are sufficiently large to admit of sub-division into tenths of degrees 

 and ranging from 0? to 130. The scale is of Negretti and Zambra's Patent 

 Porcelain, having the figures etched upon it, and burnt in a permanent black. 

 It is a reliable comparative or reference thermometer, adapted for almost any 

 ordinary purpose, and cannot be injuriously affected by any chemical action 

 arising from air or sea- water. (Fig. 34). This thermometer is employed in 



D 



