582 
PROFESSOR FORBES ON THE TEMPERATURES 
hours’ labour will suffice for the rest, and the computations are of the simplest cha- 
racter. How far the method might be applicable to thermometers of extremely fine 
bore, I am not prepared to say. 
In all cases in which this thermometer (which I designate Troughton, J. D. F.) 
has been used, which is in by far the majority of cases, we have simply to apply the 
above corrections *. 
The next thermometer we have to do with is that of Crichton, sen., already men- 
tioned, on which one or two determinations depend. Notwithstanding the character 
of the maker, it seems to have been constructed with more regard to neatness than 
accuracy, as the following comparison with Troughton J. D. F. will show, which 
were obtained by the most unexceptionable of all modes of comparing thermometers, 
by plunging them in natural hot and cold springs. The scale only goes as high as 125°. 
The following comparisons are arranged in the order of temperatures. I have in- 
serted a verification of the freezing point, which had fortunately been made on the 
27th of January 1835, the instrument having been broken by a fall at the moment of 
my return to London from the Pyrenees. These comparisons are important to be 
preserved for another reason, since they form the best possible check upon the care 
observed in reading the standard thermometer, an operation during which consider- 
able errors (as of 5° or 10°) may by chance occur unchecked. As this Table, then, 
may be made to serve the purpose of verification, I shall omit the repetition of them 
in detailing the observations at large. 
No. 
Spring. 
Crichton. 
Troughton 
reduced. 
| Error of j 
Crichton, j 
1. 
Melting snow 
32-0 
32-0 
° 1 
o-o 
2. 
Cold spring, St. Sauveur 
50-3 
49-5 
+ 0-8 
3. 
St. Sauveur, Hontalade 
69-3 
68-5 
+ 0-8 
4. 
Bagneres, Sources des Jeux 
91*2 
89-4 
+ 1-8 
5. 
Cauteretz, Petit St. Sauveur 
92-5 
90-6 
+ 1-9 
6. 
Las Escaldas, Source Merlat 
92-5 
90-7 
+ 1-8 
7. 
Las Escaldas, Grande Source 
92-7 
90-9 
+ 1-8 
8. 
Bagneres, Foulon 
94-7 
93-1 
+ 1-6 
9- 
Bareges, Polard 
100-3 
97-9 
+ 2-4 
10. 
Cauteretz, Railliere 
104-0 
101-9 
+ 2-1 
11. 
Dorres 
106-5 
104-4 
+ 2-1 
12. 
Las Escaldas, Source Colomer 
109-2 
107-1 
+ 2-1 
13. 
Arles, Maujolet. 
111-4 
1093 
+ 2-1 
14. 
Bagn&res, St. Roch 
111-8 
109-4 
+ 2-4 
15. 
Cauteretz, La Poze 
112-7 
110-3 
+ 2-4 
16. 
Bagneres de Luchon, La Reine .... 
112-8 
110-6 
+ 2-2 
17. 
Cauteretz, Bois 
114-7 
112-3 
+ 2-4 
18. 
Cauteretz, La Nouvelle Poze 
116-0 
113-5 
+ 2-5 
19. 
Bagneres, La Reine 
117-0 
114-0 
+ 3-0 
20. 
Bagneres, Roc de Lanne 
118-0 
115-2 
+ 2-8 
21. 
Bagneres, Dauphin 
121-8 
119-0 
4- 2-8 
* We have already seen that the correction for the inclination of the thermometer, owing to the pressure of 
the column of mercury, is almost insensible. It is to he understood, however, that in all the experiments 
which follow, made in France (1835), the scale was held horizontally, unless otherwise noted. 
