1830 .] 
Velocity of Sound. 
309 
Observers. 
Parry, 
Academicians, 
Gregory, 
Arago, 
Moll, 
Goldingliara, 
Temp. 
Fahr. 
Observed in 
Eng. feet. 
Computed in 
Eng. feet. 
Diff. feet. 
—17°, 72 
1034, 
1031,5 
-2,5 
+ t2 , 8 
1103,5 
1101,6 
-1,9 
48 ,62 
1107, 
1103,1 
+ 1,1 
6*0 ,62 
ill 8,4 
1121,5 
+3,1 
32 
1080,4 
1089,4 
+0,0 
32 
1080,9 
1089,4 
—0,5 
Mean difference, +0,12 
I bare no more time to devote to this part of the communication, than just 
to notice the extreme minuteness of the mean difference of our theory, only l§ 
inch, compared with that of the old, amounting to 53 metres, or 174 feet. Laplace 
has, indeed, contrived to reduce this difference to 13 or 14 feet, hy an ingenious, 
but very questionable, hypothetical assumption. The theory from which I have 
deduced the preceding formula requires no such assistance; nor I believe any 
thing beyond the simple definition of an air, 
2. — Diminution of Temperature. 
Let us now turn our attention to the other formula!. Supposing/ the Fahr. 
Temp, at the higher station, F. being that at the lower, and substituting of S. and $ 
their values in (2) and (3), we get, 
rh (f + 448) 
=320,1261785 
-(r)‘ } ■ 
P x J 80 
8Jx x 
(/+ 448) 1 ; and F — / = — — = nearly. (5) 
rh 326 ^ 
From the latter of these theorems it appears that the Fahr. Temp, decreases 
uniformly at the rate of 1° for every 326* feet. The difference may, therefore, be 
easily computed : “ Take a T £ 5 th of the altitude in yards, substract a ^tli of this 
from itself; and then add ^ths of the part so substracted.” Thus, if the altitude 
was 7600 yards : — 
76 
-7, 6 
+1,52 
60°, 92 
And in centigrade degrees— “To a T * 5 th of the Alt. in fathoms, add twice a T | 5 th 
itself, and then a of this correction.” For example, in the preceding m- 
of 
stance : — 
,38 
>76 
,076 
38°, 836 
Applying this rule to the cases extracted by Mr. Ivory from Ramond s eo lectmn 
of observations, we shall find it agree with the observations, much better than the 
observations probably by different individuals, at the same place, agree with one 
another, as the following table shews: 
Places. 
Lussac’s Ascent, 
Chimborazo, 
Montblanc, Geneva, 
Pic de Teneriffe, 
Montblanc, Chamouny, 
Ditto ditto, 
Etna, 
* These computations, and those that follow, are extracted from a letter la which 
the metre was reckoned to be 3,281 English feet. 
Heights 
Differences 
of Temp. 
Cent. Differences. 
Mean 
yards. 
observed . 
computed. 
Difference* 
7630 
40°, 3 
39°, 0 
—1.3 
6427 
26 ,9 
32 ,8 
+5,9 
f 4782 
31 ,2 
24 ,4 
—6,8 
}-5,8 
| 4782 
29 ,2 
• # 
—4,8 
4077 
16 ,5 
20 ,8 
-5,1 
+4,3 
4070 
25 ,9 
20 ,8 
1 — 5,5 
3540 
26 ,6 
18,7 
18 ,1 
— 5,8 
J * 
—0,6 
