Disirihition of Heat over the Globe. 13 
whose temperature suffered no change but from permanent 
causes. These were in the part of the great ocean commonly 
called the Pacific Ocean, from 40° of South to 45° of North la- 
titude, and in the part of the Atlantic Ocean, between the pa- 
rallels of 45° and 80®, from the coasts of England to the Gulf 
Stream, the high temperature of which was first determined by 
Sir Charles Blagden. Kirwan tried to determine for every 
month the mean temperature of these seas at different degrees of 
latitude ; and these results afforded him terms of comparison 
with the mean temperatures observed on the solid part of the ter- 
restrial globe. It is easy to conceive, that this method has 
no other object, but to distinguish in climates that is in the to- 
tal effect of calorific influences, that which is due to the imme- 
diate action of the sun on a single point of the globe. Kirwan 
first considers the earth as uniformly covered with a thick stra- 
tum of water, and he then compares the temperatures of this 
water at different latitudes, with observations, at the surface of 
continents indented with mountains, and unequally prolonged 
towards the poles. 
This interesting investigation may enable us to appreciate the 
influence of local causes, and the effect which arises from the 
position of seas, on account of the unequal capacity of water and 
earth for absorbing heat. It is even better fitted for this ob- 
ject than the Method of‘ Means deduced from a great number 
of observations made under different meridians ; but in the ac- 
tual state of our physical knowledge, the method proposed by 
Kirwan cannot be followed. A small number of observations 
made far from the coasts, in the course of a month, fixes, with- 
out doubt, the mean annual temperature of the sea at its surface, 
and, on account of the slowness with which a great mass of wa- 
ter follows the changes of the temperature of the surrounding 
air, the extent of variations in the course of a month is smaller 
in the ocean than in the atmosphere : But it is still greatly to be 
desired *, that we should be able to indicate by direct experi- 
ence, for every parallel, and for every month, the m^an tempe- 
rature of the ocean under the temperate zone. The scheme 
which Kirwan has formed for the extent of the seas, that ought la 
* See my Relation Historiqne, tom. i. 
