CHAP. II. ] FROM PORTSMOUTH TO TENERIFFE. 155 
Observations made at subsequent periods in the same district 
gave a much better insight into the nature of this change. 
Throughout the year meteorological observations were taken 
with great care and regularity. The barometer, the wet and 
dry bulb thermometer in air, the temperature of the sea-sur- 
face, the direction and force of the wind, and the proportion 
of cloud and the general state of the weather, were registered 
not less than once in two hours by the officers of the watch. 
Whenever there was any marked peculiarity in atmospheric 
condition or in the temperature of the sea, or any suspicion 
that there might be cause for such, observations were made 
hourly, and often half-hourly. 
It must be remembered, however, that, owing to the ship 
constantly changing her position, and passing into different lat- 
itudes, and being subjected to different local conditions, these 
observations have not the kind of value of a series of observa- 
tions taken at a single spot, but must be regarded as isolated 
observations, each good only for the position and date at which 
it was taken. As such, however, their importance can scarcely 
be overrated, in their bearings upon the discussion of the ques- 
tions regarding the movement of air and water, and the con- 
ditions of climate affecting the maintenance and distribution of 
living beings, which it was our mission to attempt to solve. 
This, of course, does not apply to series of observations extend- 
ing over a considerable time at one place, such as those taken 
in harbor at Bermudas, Halifax, ete. 
The number of separate observations was so great—amount- 
ing during the twelve months from the 1st of December, 1872, to 
the corresponding date in 1873 to upward of 50,000—and would 
have occupied so much space in a tabular form, that it has 
been thought preferable, in this preliminary sketch, to reduce 
some of the general results to diagrams. In a series of twelve 
plates, accordingly, the results are given for the several months. 
The darker vertical lines on the plates indicate the hour of 4 
