cHaAP. V1. ] DEEP-SEA TEMPERATURES. DONT 
this way imperceptible by any direct effect upon 
navigation beyond the 45th parallel of north latitude, 
a peculiarity which has produced and still produces 
ereat misconceptions as to its real character. 
The mode of determining the surface temperature 
of the ocean is sufficiently simple. A bucket is 
let down from the deck of the vessel, dashed about 
for a little in the water to equalize the temperature, 
and filled from a depth of a foot or so below the sur- 
face. ‘The temperature of the water in the bucket is 
then taken by an ordinary thermometer, whose error 
is known. A common thermometer of the Kew 
Observatory pattern graduated to Fahrenheit degrees 
can be read with a little practice to a quarter of a 
degree, and a good-sized centigrade thermometer to 
a tenth. Observations of surface-temperature are 
usually made every two hours, the temperature of 
the air being taken with each observation, and the 
latitude and longitude noted at noon, or more fre- 
quently by dead reckoning if required. 
Every observation of the surface-temperature of 
the sea taken accurately and accompanied by an 
equally exact note of the date, the geographical 
position, and the temperature of the air, is of value. 
The surface observations taken from H.M.S. ‘ Por- 
cupine’ during her dredging cruise, in the summer 
of 1869, are given in Appendix A. 
The surface-temperature of the North Atlantic has 
been the subject of almost an infinite number of such 
observations, more or less accurate. Dr. Petermann, 
in a valuable paper on the northern extension of 
the Gulf-stream, reduces the means of more than a 
hundred thousand of these, and deduces the scheme 
