45, COBNHILL, E.G., AND 122, EEGENT STREET, W., LONDON. 37 



FIG 40. 



48. Negretti and Zambra's Patent Self-registering Standard 

 Maximum Thermometer, consists of a tube of mercury mounted on an 

 engraved scale, as shown in fig 40. The thermometer tube above the mercury 

 is entirely free from air ; and at the point (A) in the bend above the ball, is 

 inserted and fixed with the blow-pipe a small piece of solid glass, or enamel, 

 which acts as a valve, allowing mercury to pass on one side of it when heat i s 

 applied ; but not allowing it to return when the thermometer cools. When 

 mercury has been once made to pass the valve, which nothing but heat can effect' 

 and has risen in the tube, the upper end of the column registers the maximum 

 temperature. To return the mercury to the btflb, we must apply a force 

 equal to that which raised it in the tube ; the force employed is gravity, and is 

 applied by simply lowering the bulb end of the thermometer, when the gravity 

 of the mercury in the tube will be sufficient to unite it with that in the bulb, and 

 thus prepare the instrument for future observation. 



Price, mounted with Negretti and Zambra's enamelled tube and Patent 



Porcelain or Opal glass Scale, fig. 40 110 



The following is an extract from the Report of the Astronomer Royal, pub- 

 lished shortly after the invention of the instrument it, however, applies more 

 strongly now, inasmuch as the intervening years have fully proved the efficiency 

 and value of this invention : - 



Report of the Astronomer Royal, May, 1852. 



" We have for several years baen very much troubled by the failures of the Maximum Self-Eegistermg 

 Thermometers, especially those exposed to the sun: the part of the tube in which the index ought to 

 slide becomes foul, apparently lined with* a coat of metal, and the index is immovable. A construction 

 invented by Messrs. Negretti and Zambra appears likely to evade this difficulty. The mercury in its 

 expansion is forced past an obstruction in the tube and does not return past in its contraction. No index 

 is required in this construction. The specimens of this instrument which we have tried answer well." 



In the Quarterly Report of the Registrar General, about the same time, there 

 is the following annotation : 



l * The form of instrument adopted during the past quarter for maximum temperature is that of 

 Negretti and Zambra, which is found to act admirably." 



J. GLAISHEE, Esq., F.R.S., in his Lectures on the Results of the Great 

 Exhibition, delivered at the Society of Arts, at the suggestion of his late 

 Royal Highness the Prince Consort, when speaking of Meteorological 

 Instruments (page 363) says : 



" In. maximum and minimum thermometers there was nothing new exhibited, although great need had 

 long existed for an effective Maximum Thermometer. Thanks to the exhibition, however, this want has 



* The whole of Negretti and Zambra's Standard Thermometers have their improved enamelled back 

 tabes and are Engine-divided on the stem. 



