46 



NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, B.C., 



black glass index. The tube is engine divided and mounted as shown in fig. 53. 

 on either N. and Z.'s patent Porcelain or Opal Glass Scales. 



Directions for using Minimum Thermometers, for the Determination of the 

 Minimum Temperature of the Air. Having caused the black index to flow to 

 the end of the column of spirit, by slightly tilting the Thermometer, bulb 

 uppermost, suspend the instrument, (in the shade with the air passing freely to 

 it on all sides) by the two plates attached for that purpose, in such manner 

 that the bulb is about half an inch lower than the end of the Thermometer 

 furthest from the bulb, then on a decrease of temperature, the spirit will 

 descend, carrying with it the index towards the bulb ; on an increase of 

 temperature, the spirit will ascend in the tube beyond the index, leaving that 

 end of the index furthest from the bulb indicating the extreme of cold or 

 Minimum temperature. To re-set the instrument, simply raise the bulb end of 

 the Thermometer a little, as before observed, and the index will again descend 

 to the end of the spirit, ready for future observation. 



Price, in mounting as fig, 53 1 1 



FIG. 54. 



64. Negretti and Zambra's Standard Terrestrial Radiation 

 Thermometer, (fig. 54). The bulb of this instrument is transparent, with the 

 divisions engraved on its stem similar to that for solar radiation. In use, to be 

 placed with its bulb fully exposed to the sky, resting on grass, with its stem 

 supported by little forks of wood. Price, 110 



FIG. 55. 



65. Negretti and Zambra's Link shaped Bulb Minimum 

 Thermometer, mounted either as a Terrestrial Radiation irstrument, fig. 55, o r 

 on a Porcelain scale as fig. 53. This peculiar form of bulb was devised by Negretti 

 and Zambra to obtain extreme sensitiveness by the large surface exposed to air. 



Price, 150 



