HEAT OR CALORIC. 5- 



After the ball has been cooling for a few minutes, the excess of 

 mercury is poured out, and the column allowed to subside. 



Sg.) To try whether the range of the mercury will be correct. 

 mmerse the ball in melting ice or snow the mercury should not 

 sink within the ball immerse it in boiling water, or, which is better, 

 in steam. In this case, the mercury should not rise so high as the 

 top of the tube and these two points, the freezing and the boiling 

 should fall higher or lower according to the use that is to be made of 

 the thermometer, for measuring high or low degrees that is, ex- 

 tremes of heat or of cold ; if intended for both, there should be 

 sufficient room both above and below these two points. 



(A.) If there be not mercury enough, warm the ball in a candle, 

 and let the column, as it reaches the summit, be united to more quick- 

 silver in a wine glass, quickly reversing and plunging the tube for that 

 purpose. 



(i.) If there be too much mercury, let a little of it be expelled, by 

 warming the ball, and then in either case, the mercury must be ad- 

 justed as regards the freezing and boiling points, by a new immer- 

 sion in melting snow or ice and in steam. 



(j.) To close the tube to exclude the atmosphere. 



Draw the end of the tube in two by the blow pipe, and it will be of 

 course hermetically sealed ; then break the fine point so that it may be 

 merely open ; next warm the ball, so that the mercury will rise and fill 

 the entire tube, and just as it is about to issue from the orifice, things 

 being previously adjusted for that purpose, direct the blowpipe flame 

 upon the point, and seal it ; if correctly done, the mercury will then roll, 

 backward and forward, without breaking the column and without im- 

 pediment. 



(k.) Final adjustment of the fixed points of freezing and boiling. 



A new exposure to the melting ice and to the steam of boiling 

 water, will now give us, by inspection of the top of the mercurial 

 column, the important points of freezing and boiling water, which 

 must be marked on the glass by a diamond or a file. 



(/.) Graduation of the instrument. The space, between freezing 

 and boiling water, is now to be divided into one hundred and eighty 

 equal parts; freezing water will be 32 and boiling water 212. 



This division is arbitrary. It was adopted by Fahrenheit of Am- 

 sterdam, after whom the thermometer, thus graduated, was called. The 

 of this scale indicated the greatest cold observed in Iceland, and it 

 was supposed to be as great as would probably ever occur in philo- 

 sophical experiments. ^The scale is extended above boiling water to 

 any desired degree, and below 0, by numbers reckoned the opposite 

 way, which are considered as minus degrees and marked with the 

 correspondent arithmetical sign, while the degrees above are written 

 without any sign. 



