45, COEKHILL, E.G., AND 122, REGENT STEEET, W., LONDON. 



31 



INSTRUMENTS FOR ASCERTAINING THE TEMPERATURE OF THE AIR. 



THEEMOMETBES. 



FIG. 31. 



37. Undoubtedly there is no instrument the use of which has so greatly 

 increased in the past few years as the Thermometer : not only is it now 

 essential to the scientific observer, the meteorologist, the physician, and the 

 chemist; but both for domestic uses and manufacturing processes a really 

 accurate thermometer is indispensable. The following is a list of the various 

 forms of Standard Thermometers manufactured by Negretti and Zambra ; all of 

 these, to ensure extreme accuracy, have their scales divided by the Prize 

 Dividing Engine (fig. 31) to which was awarded a Prize Medal at the Great 

 Exhibition of 1851, and is described in the Report of the Jurors as follows : 



" This is a beautifully contrived Divider on Ramsden's principle, with a long fine steel 

 screw. The novelties are first, the wheel at the screw head, which is divided into 400 parts, 

 and has cut upon its circumference (which is made broad) a helix screw, in the thread of 

 which runs a detent, carried along by the run of the thread till it meets a stop clamped on 

 the helix at a definite point. This arrests the screw at this point of the motion. 

 A Prize Medal was awarded." 



Messrs. Negretti and Zambra supply Dividing Engines made on the above 

 principle both for circular and straight line divisions. 



Price . . 35 to 150 



NOTE. From Report of the Juries of the Exhibition of 1851. " Negretti and Zambra 

 are the only exhibitors in the British portion who have sent Thermometers with their stem* 

 graduated the only safe instruments for delicate experiments." 



