Several interesting facts will be shown by the consideration of this document:—
1st. The great range of the variations of surface temperatures in the same day under the influence of the burning sun of Syria; thus, on May 2nd the temperature on the surface was: 73°·4 at 8.45 in the morning; 79°·25 at 2.30 p.m., and 69°·35 at 9 p.m., a coolness of 6 degrees in six hours and a half, a coolness parallel to that of the air above and caused by the action of a strong breeze from the north-west.[1]
2nd. The relatively inconsiderable depth of the zone subject to diurnal variations is scarcely 15 metres, not more than in the Lake of Geneva, where the mean temperature of the air above is, however, very much lower.[2] Thus, at Tiberias the temperature of the water, which is 67°·4 to 69°·44 at 32·8 feet in depth, falls rapidly to the number of 61°·70 to 63°·05 at 49·21 feet in depth.
3rd. The uniform temperature (59°) of the deep beds, between 65 feet and 131·24 feet; it is only in neighbourhoods of this last level that the thermometer shows a slight diminution of 0°·9 to 58°·1.
This last fact requires that we should pause an instant; Forel has demonstrated that if we put on one side the figures of the upper bed of 10 metres in depth, which is influenced by the temperature of the air above, we prove that the water of the deep beds gets heated much more quickly in the shallow lakes.[3] Now, if we compare our results with those obtained by the learned Swiss professor, we shall see that the number of 58°·1 for a level of 131·24 feet is much higher than the average number observed in the Swiss lakes, a number which oscillated during the summer of 1880, for instance, between 41°·36 and 46°·4. This last temperature was taken in the Lake of Morat, the one which, as regards depth, most resembles the Lake of Tiberias. The adjoining table will make these facts clearer:—
| Tiberias = 137 feet.[4] May. |
Morat = 157 feet. August. |
Zurich = 469 feet. August. | |||||
| o | o | o | o | ||||
| — | 73·04 | Fah. | 66·38 | Fah. | 67·46 | Fah. | |
| 16·4 | feet | 71·15 | 65·84 | — | |||
| 32·81 | " | 68·54 | 64·40 | 66·20 | |||
| 49·21 | " | 62·24 | 51·44 | — | |||
| 62·62 | " | 59·00 | 49·28 | 45·68 | |||
| 82·02 | " | 59·00 | 48·02 | — | |||
| 98·43 | " | 59·00 | 47·30 | 42·80 | |||
| 131·24 | " | 58·10 | 46·40 | 41·36 | |||
- ↑ During the first four days of my stay at Tiberias, that is to say, the 29th and 30th of April and the 1st and 2nd of May, this fresh breeze rose regularly between 3 and 4 o'clock in the afternoon.
- ↑ All the following figures are given after correction.
- ↑ Forel, "Les Faunes profondes des Lacs suisses," p. 23.
- ↑ Approximate mean depth, see p. 216.
