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of account tlie fact that there is on the whole an outflow of pure 
Mediterranean water at the bottom which affects the temperature 
and density of the Atlantic water outside. In sea water, owing to 
its saltness, convection currents are set up more actively by cooling 
than is found to be the case in fresh water. In lakes, however, 
and especially in those situated in mountainous districts, the pro- 
duction of convection currents is powerfully assisted by local dif- 
ferences of climate. These are due to differences of exposure, to 
radiation, and to prevailing winds. Such local differences of climate 
produce local differences of temperature, and consequently of density 
in the superficial layers. If we compare, for instance, the obser- 
vations made at Ardlui and at Inversnaid on 15th October, we find 
that the mean temperature of the first 20 fathoms is 48° - 24 at Inver- 
snaid, and only 46° *58 F. at Ardlui. The stations are only three 
miles apart, and yet there is a difference of 1°*66 F. in the mean 
temperature of the first 20 fathoms. Another cause affects the dis- 
tribution of temperature in a lake, namely, the drainage, but this 
more particularly affects shallow lakes or basins. It is probable 
that the most powerful means of supply and removal of heat is 
direct radiation. The most powerful mixing agency is the wind. 
I hope, with Mr Morrison’s assistance, to secure monthly observa- 
tions during the coming winter and spring, the results of which 
cannot fail to be interesting. 
2. On Oceanic Shoals discovered in the s.s. “ Dacia ” in 
October 1883. By J. Y. Buchanan, F.B.S.E.* (Plate XII.) 
Owing to the kindness of the India Bubber, Gutta Percha, and 
Telegraph Works Company of Silvertown, and especially of their 
engineer-in-chief, Mr Pobert Kaye Gray, I was enabled to accompany 
their expedition for laying the telegraph cable between Cadiz and 
the Canary Islands. It consisted of two steamers belonging to the 
company, the “Dacia” and the “ International”; and I was allotted 
a place and all facilities for working on board the “Dacia,” where 
Mr Gray had charge. I joined the expedition at Cadiz on 3rd 
October 1883. 
* A portion of the narrative part of this paper appeared as a correspondence 
in the Times of 7th December 1883. 
