[ 510 ] 
LXXVIIL — On the Heat of Vapours and on Astronomical Refrac- 
tions. By John William Lubbock, Esq.^ Treas. R,S. F.R.A,S. 
and F,L,S.) Vice-Chancellor of the University of London^ ^c, 
[Continued from p. 441.] 
ON THE PRESSURE OF STEAM. 
^1 most accurate and extensive experiments by which the ac- 
curacy of these relations can be tested are those which have been 
made upon the conditions of steam. The following are the experi- 
ments of Arago and Dulong, as recorded in tom. x. of the Memoir es 
de V Institute p. 231 ; together with the temperatures calculated by 
the best empirical formulae*. 
Nos. des ob- 
servations. 
Elasticite 
en mdtres 
de mer- 
cure k 0°. 
Elasticite 
en at- 
mosph. de 
Om-76. 
Tempe- 
rature 
observee. 
Temperature 
calculee par 
la formule 
de Tredgold. 
Temperature 
calculee par 
la formule 
de Roche 
cdeff. moyen. 
Temperature 
calculee par 
la formule 
de Coriolis. 
Temperature 
calculee par 
la formule 
adoptee. 
Cent. 
Cent. 
Cent. 
Cent. 
Cent. 
1 
1-62916 
2-14 
123°-7 
123°-54 
123-58 
123°45 
122°97 
3 
2-1816 
2-8705 
133-3 
133-54 
133-43 
133-34 
132-9 
5 
3-4759 
4-5735 
149-7 
150-39 
150-23 
150-3 
149-77 
8 
4-9383 
6-4977 
163-4 
164-06 
163-9 
164-1 
163-47 
9 
5-6054 
7-3755 
168-5 
169-07 
169-09 
169-3 
168-7 
15 
8-840 
11-632 
188-5 
188-44 
188-63 
189-02 
188-6 
21 
13-061 
17-185 
206-8 
206-15 
207-04 
207-43 
207-2 
22 
13-137 
17-285 
207-4 
206-3 
206-94 
207-68 
207-5 
25 
14-0634 
18-504 
210-5 
209-55 
210-3 
211-06 
210-8 
28 
16-3816 
21-555 
218-4 
216-29 
218-01 
218-66 
218-5 
30 
18-1894 
23-934 
224-15 
222-09 
233-4 
224-0 
224-02 
There are reasons which make it probable that in inquiries of this 
nature the scale of temperature as indicated by the expansion of air 
is to be preferred, although the difference between the indications 
of a mercury thermometer with that of air is not considerable. 
The following table is given by M. Pouillet (FMmens de Phy- 
sique^ vol. i. p. 259) for the centigrade scale : 
Temperatures indiquees par 
le therm, k mercure, a en- 
veloppe de verre. 
Temperatures indiquees par 
un therm, k air, et corrigees 
de la dilatation du verre. 
Volumes correspondans 
d’une meme masse d’air. 
- 36 
- 36° 
0-8650 
0 
0 
1-0000 
100 
100 
1-3750 
150 
148-70 
1-5576 
200 
197-05 
1-7389 
250 
245-05 
1-9189 
300 
292-70 
2-0976 
Ebull. du mere. 360 
350-00 
2-3125 
[* Many of the results stated in the table of the French chemists are absolutely iden- 
tical with those which had been published by Mr. Philip Taylor in 1822. See his Paper 
in the Philosophical Magazine, First Series, vol. lx. p. 452., and the accompanying en- 
graved Table of his experimental results, — Edit.] 
