xxx ii INTRODUCTION. 



rature was but seldom found above the freezing point of water ; the 

 lowest temperature was 22. From the low temperature of both 

 water and air, it will be perceived that when ice is once formed, it 

 can seldom be melted while it remains in these high latitudes : this 

 will account for the large masses which are almost constantly accu- 

 mulating from the depositions in the form of snow, sleet,, or fog. 



The winds which prevailed were from the northwest and south- 

 west, until we had passed to the westward of the meridian of 160 

 east, when we had a change from the eastward, with better weather. 

 The mean degree of moisture was '890. The photometer was ex- 

 posed for the 24 hours for several days : it fell to 19 for the night 

 hours, and rose to 93 in the day : from this it is evident that the 

 intensity of light in the southern hemisphere is not as great as it is 

 represented to be in the northern. 



The mean solar radiation was 4 -7 ; the greatest difference between 

 the sun and shade 9; least 1. A thermometer placed on the black 

 hammock-cloth in the sun rose only to 3G, that in the shade being 

 30. This shows a remarkable difference in the power of the sun's 

 rays between the southern and northern hemispheres. Captain 

 Scoresby and other Arctic navigators state, that the temperature in 

 the sun frequently rose to that of melting pitch, while it was below 

 the freezing point in the shade. 



It will be seen, on referring to our first cruise to the south, repre- 

 sented on Plate VI., page 138, in the longitude of Cape Horn, that the 

 same results were had : the barometric column decreased in altitude 

 as we reached the higher latitudes, and the thermometers in the air 

 followed that of the water, until masses of ice intervened. The degree 

 of moisture on that cruise was '935. From an examination of the 

 temperature of the southern hemisphere, I have become satisfied 

 that it is more equable than the northern ; of this we have had 

 many proofs, and the observations I have had access to fully cor- 

 roborate it: the fact of the thermometer having varied but a few 

 degrees during the summer months, the power of the sun's rays not 

 being so great, and the temperature not descending so low during 

 winter, together with a much higher mean annual temperature, and 

 a much less range, all tend to satisfy me that such is the case. 



In the Narrative, I have mentioned several gales which occurred 

 during this southern cruise : the progress of only one I have been able 

 to trace satisfactorily, in consequence of the four vessels of the squadron 

 having been separated some distance from each other. I have refe- 



