620 
ME. J. PBESTWICH ON STTBMAEINE TEMPEEATTJEES. 
in the Mediterranean by Saussuke in 1780, of 55 0, 8 F. at 944 feet, and 55° - 5 at 
1918 feet, remain substantially correct to the present day. It was, however, D’Urville’s 
more extended observations in 1826 that made better known the fact that the tempe- 
rature decreased from the surface down to 200 brasses (1066 feet), below which it 
remained constant at about 13° C., or between 54° and 55° F. Still his greatest depth 
did not exceed 3189 feet; but Berard in 1831 extended the observations to a depth of 
6377 feet, and still found the same degree of temperature. 
Aime further showed, from a series of soundings made during 1840-44 in the western 
basin of the Mediterranean, between Marseilles and Algiers, that the diurnal variation 
of temperature ceases to be sensible at 16 to 18 metres, and the annual variation at 
300 to 400 metres. The mean of his series of observations gave the following results : — 
Mean Annual Temperature of the Mediterranean at different depths. 
Depth. 
Temperature. 
Extreme monthly variations. 
Surface. 
18*2 Cent. 
10°-2 Cent. 
25 metres. 
16-3 
6-3 
CD 
o 
14-4 
2-8 
100 „ 
13-7 
2-0 
200 „ 
13-0 
1-0 
350 „ 
12-6 
0-0 
This temperature of 12°-6 (54°-7 F.) he showed to be that of the mean of the winter 
months (or rather that of the months of January, March, and April) of the area; and 
he was of opinion that the same temperature obtained at greater depths, referring 
in support of that opinion to other and deeper soundings by Berard. The fol- 
lowing observations by the latter, made between the Balearic Islands and Algeria, are 
extracted from D’Urville’s tables : — 
Depths of | SurfaCein August 
AT rwom nDT* 
variable •< 
temperature. | 
Depths of 
uniform <( 
temperature. | 
November 
At depth of 40 brasses in October 
55 10 55 55 
„ 600 
600 
750 
1200 
November 
June 
November 
June 
27-1 Cent. 
14-6 
16-5 
14-9 
13 
13 
13 
13 
This gives the rather higher reading of 55°*4 at depths ; but whether arising from 
Berard using less perfect instruments or from an actual difference of temperature on this 
southern side of the Mediterranean, is uncertain. The marked agreement between the 
observations of Berard in 1831-32 and those of the ‘Porcupine’ expedition in 1870, 
leads me to suppose that the latter may be the influencing cause. 
D’Urville’s observations, which were made further north in the western Mediter- 
ranean than those of Berard, agree more closely with those of Aime. Thus he found — 
