Thermometer 637

Correspondence of the Thermometers of Fahrenheit and Reaumur, and that of Celsius, or the Centigrade Thermometer of the modern French Chemists.

Fahr.

Reaum.

Celsius.

Fahr.

Reaum.

Celsius.

Fahr.

Reaum.

Celsius.

Fahr.

Reaum.

Celsius.

Fahr.

Reaum.

■ Celsius.

212

80.

100.

161

57.3

71.6

110

34.6

43.3

59

12.

15.

8

10.6

13.3

211

79.5

99.4

160

56.8

71.1

109

34.2

42.7

58

11.5

14.4

7

11.1

13.8

210

79.1

98.8

159

56.4

7 0.5

108

33.7

42.2

57

11.1

13.8

6

11.5

14.4

209

78.6

98.3

158

56.

70.

107

33.3

41.6

56

10.6

13.3

5

12.

15.

208

7 8.2

97.7

157

55.5

69.4

106

32.8

41.1

55

102

12.7

4

12.4

15.5

207

77.7

97.2

156

55.1

68.8

105

32.4

40.5

54

9.7

12.2

3

12.8

16.1

206

77.3

96.6

155

54.6

68.3

104

32.

40.

53

9.3

11.6

2

13.3

16.6

205

76.8

96.1

154

54.2

67.7

103

31.5

39.4

52

8.8

11.1

1

13.7

17.2

204

76.4

96.5

153

53.7

67.2

102

31.1

38.8

51

8.4

10.5

0

14.2

17.7

203

76.

95.

152

53.3

66.6

101

30.6

38.3

50

8.

10.

1

14.6

18.3

202

75.5

94.4

151

52.8

66.1

100

30.2

37.7

49

7.5

9.4

2

15.1

18.8

201

75.1

93.8

150

52.4

65.5

99

29.7

37.2

48

7.1

8.8

3

15.5

19.4

200

74.6

93.3

149

52.

65.

98

29.3

36.6

47

6.6

8.3

4

16.

20.

199

74.2

92.7

148

51.5

61.4

97

28.8

36.1

46

6.2

7.7

5

16.4

20.5

198

73.7

92.2

147

51.1

63.8

96

28.4

35.5

45

5.7

7.2

6

16.8

21.1

197

73.3

91.6

146

50.6

63.3

95

28.

35.

44

5.3

6.6

7

17.3

21.6

196

72.8

91.1

145

50.2

62.7

94

27.5

34.4

43

4.8

6.1

8

17.7

22.2

195

72.4

90.5

144

49.7

62.2

93

27.1

33.8

42

4.4

5.5

9

18.2

22.7

194

72.

90.

143

49.3

61.6

92

26.6

33.3

41

4.

5.

10

18.6

23.3

193

71.5

89.4

142

48.8

61.1

91

26.2

32.7

40

3.5

4.4

11

19.1

23.8

192

71.1

88.8

141

48.4

60.5

90

25.7

32.2

39

3.1

3.8

12

19.5

24.4

191

70.6

88.3

140

48.

60.

89

25.3

31.6

38

2.6

3.3

13

20.

25.

190

70.2

87.7

139

47.5

59.4

88

24.8

31.1

37

2.2

2.7

14

20.4

25.5

189

69.7

87.2

138

47.1

58.8

87

21.4

30.5

36

1.7

2.2

15

20.8

26 1

188

69.3

86.6

137

46.6

58.3

86

24.

30.

35

1.3

1.6

16

21.3

26.6

187

68.8

86.1

136

46.2

57.7

85

23.5

29.4

34

0.8

1.1

17

21.7

27.2

186

68.4

85.5

135

45.7

57.2

84

23.1

28.8

33

0.4

0.5

18

22.2

27.7

185

68.

85.

134

45.3

56.6

83

22.6

28.3

32

0.

0.

19

22.6

28.3

184

67.5

84.4

133

44.9

56.1

82

22.2

27.7

31

0.4

0.5

20

23.1

28.8

183

67.1

83.8

132

44.4

55.5

81

21.7

27.2

30

0.8

1.1

21

23.5

29.4

182

66.6

83.3

131

44.

55.

80

21.3

26.6

29

1.3

1.6

22

24.

30.

181

66.2

82.7

130

43.5

54.4

79

20.8

26.1

28

1.7

2.2

23

24.4

30.5

180

65.7

82.2

129

43.1

53.8

78

20.4

25.5

27

2.2

2.7

24

24.8

31.1

179

65.3

81.6

128

42.6

53.3

77

20.

25.

26

2.6

3.3

25

25.3

31.6

178

64.8

81.1

127

42.2

52.7

76

19.5

24.4

25

3.1

3.8

26

25.7

32.2

177

61.4

80.5

126

41.7

52.2

75

19.1

23.8

24

3.5

4.4

27

26.2

32.7

176

64.

80.

125

41.3

51.6

74

18.6

23.3

23

4.

5.

28

26.6

33.3

175

63.5

79.4

124

40.8

51.1

73

18.2

22.7

22

4.4

5.5

29

27.1

33.8

174

63.1

78.8

123

40.4

50.5

72

17.7

22.2

21

4.8

6.1

30

27.5

34.4

173

62.6

78.3

122

40.

50.

71

17.3

21.6

20

5.3

6.6

31

28.

35.

172

62.2

77.7

121

39.5

49.4

70

16.8

21.1

19

5.7

7.2

32

28.4

35.5

171

61.7

77.2

120

39.1

48.8

69

16.4

20.5

18

6.2

7.7

33

28.8

36.1

170

61.3

76.6

119

38.6

48.3

68

16.

20.

17

6.6

8.3

34

29.5

36.6

169

60.8

76.1

1 1 8

38.2

47.7

67

15.5

19.4

16

7.1

8.8

35

29.7

37.2

168

60.4

75.5

117

37.7

47.2

66

15.1

18.8

15

7.5

9.4

36

30.2

37.7

167

60.

75.

116

3

46.6

65

14.6

18.3

14

8.

10.

37

30.6

38.3

166

59.5

74.4

115

36.8

46.1

61

14.2

17.7

13

8.4

10.5

38

31.1

38.8

165

59.1

73.8

114

36.4

45.5

63

13.7

17.2

12

8.8

11.1

39

31.5

39.4

164

58.6

73.3

113

38.

45.

62

13.3

16.6

11

9.3

11.6

40

32.

40.

163

58.2

72.7

112

3 5.5

44.4

61

12.8

16.1

10

9.7

12.2

162

57.7

72.2

111

35.1

43.8

60

12.4

15.5

9

10.2

12.7

where it terminates in a knee bent at right angles. The float-wire, by means of an eye at h, moves easily along the small harpsichord wire g h. ll are two indexes made of thin black oiled silk, which slide upwards or downwards with a force of not more than two grains. The one placed above the knee points out the greatest rise, and the one placed below it points out the greatest fall, of the thermometer. When the instrument is to be prepared for an observation, both indexes are to be brought close to the knee h. It is evident, that when the mercury rises, the float and float-wire, which can be moved with the smallest force, will be pushed upwards till the mercury becomes stationary. As the knee of the float-wire moves upwards, it will carry along with it the upper index l. When the mercury again subsides, it leaves the index at the highest point at which it was raised, for it will not descend by its own weight: as the mercury falls, the float-wire does the same; it therefore brings along with it the lower index l, and continues to depress it till it again becomes stationary, or ascends in the tube; in which case it leaves the lower index behind it, as it had formerly left the upper. The scale to which the indexes point is placed parallel to the slender harpsichord wire.

That the scale and indexes may not be injured by the wind and rain, a cylindrical glass cover, close at top, and made so as exactly to fit the part gf, is placed over it. As a knowledge of the correspondence between the thermometers of Fahrenheit, Reaumur, and Celsius, are indispensable to the comprehension of the scientific labours of the French and German philosophers and authors, whether in the original languages, or the English translations, we have inserted a table in which the degree of any given temperature under 212° of Fahrenheit is expressed by those of Reaumur and Celsius: we omit De Lisle's, its use being confined to Russia. As, however, higher degrees of temperature may be required than those given in the table, the following rules are given for changing the degrees of any one of the scales into equivalent degrees of another; viz. each degree of Fahrenheit is equal to four-ninths of one of Reaumur; as Reaumur, however, reckons his degrees from the freezing point, and Fahrenheit 32° below this point, we must, when the number of Fahrenheit's degrees to be reduced indicate a temperature above the freezing-point, first deduct 32, then multiply the remainder by 4, and divide the product by 9. The quotient is the corresponding number of degrees on Reaumur's scale.

If the temperature indicated was less than the freezing point, we must also be careful to take the actual number of degrees, reckoning from the freezing point. Thus 4 degrees above Fahrenheit's zero is 28 below his freezing point; and this is the number to be reduced to Reaumur's scale.

Each degree of Reaumur is equal to 2$ of one of Fahrenheit. Multiply the given number of degrees of Reaumur by 9, and divide the product by 4. If the degrees of Reaumur were minus, the quotient must be deducted from 32, and the remainder will be the equivalent degrees of Fahrenheit. If the given degrees were not minus, the quotient must be added to 32 degrees, and the sum will be the equivalent sought.

Each degree of Fahrenheit is equal to 5/8 of one of the centigrade. Proceed as in the case of Fahrenheit and Reaumur, multiplying, however, by 5, and dividing by 9.

Each degree of Reaumur is equal to 1 1/4 of the centigrade. Multiply the given number of degrees by 5, divide the product by 4, and the quotient will be the equivalent number of degrees on the centigrade scale.

Each degree of the centigrade scale is equal to four-fifths of Reaumur. Multiply the given number of degrees of the centigrade by 4, and divide the product by 5; the quotient will be the equivalent number of degrees on Reaumur's scale.

The different degrees of expansibility of dissimilar metals by the same increase of temperature, is well known, and has been usefully employed to produce compensation in the regulators of time-keepers; and recently a very sensible and convenient thermometer has been made on the same principle.

Thermometer 638

The one from which we made the diagram on the next page, is contained in a common-sized pocket-watch, and indicates the temperature from 30o below zero to 80° Reaumur, equal to the extent from zero, to 212° on Fahrenheit's scale.

It consists of a slip of steel on a slip of brass attached together, and bent with the brass inwards, into a circular form a a, and fixed to the frame of the watch at b, immediately behind the dial. One end of this circular piece is bent inwards at c, and acts upon a lever, e f, of the third order. The lever moves upon a pivot atf, is furnished with an adjusting screw d, and a toothed segment e. The teeth of this segment act upon the teeth of a small pinion g, to the projecting pivot of which an index h is attached.

The action of this little instrument is obvious; for as the interior portion of the compound circular piece is of brass, which is more expansible than the exterior, which is of steel, an increase of heat will cause the ring to open; but in opening it acts upon the lever, and by that means turns the index, which points out by the graduated circle on the face of the watch the quantity of increase. On the contrary, when a decrease of heat takes place, the ring will have a tendency to close, and the lever being kept up to it by a small spring on the opposite side, acts upon the index, and points the quantity of decrease in the temperature. This thermometer indicates a change of temperature much quicker than the common mercurial thermometer, owing to the metals being better conductors of caloric, than wood or glass, the substances of which they are usually manufactured.