xvi 



INTRODUCTION. 



forming so large and constant a portion of the interest of a polar 

 voyage. In the journal from which these abstracts were made, the 

 temperature of the air and of the sea- water was noted every two hours, 

 and the height of the mercury in the barometer every four hours, 

 throughout the voyage ; and the abstracts were carefully and separately 

 arranged by Lieutenant Nias and Mr. Boss # . The whole of the tem- 

 peratures were registered by Fahrenheit's thermometer, and the signs + 

 and — signify above or below zero of that scale. When neither of these 

 signs is attached, the temperature is to be understood as positive, or 

 above zero, except in those columns of the abstracts where a continued 

 series of low temperatures occurs. To avoid needless repetition also 

 in the course of the Narrative, it may here be added that the whole 

 of the bearings are the true ones, the Dips of the Magnetic Needle 

 North, the Latitudes North, and the Longitudes West of the meridian 

 of Greenwich, unless otherwise expressly noticed at the time. 



The temperature of the sea below the surface was sometimes ob- 

 tained by Six's self-registering thermometer attached to the deep-sea 

 lead ; but more commonly (in consequence of the frequent failure of 

 that instrument when exposed to sudden changes) by bringing up 

 some water in the bottle contrived by Dr. Marcet, and already de- 

 scribed in the Introduction to the Narrative of the former Voyage. 

 This simple and useful apparatus was now somewhat improved by a 

 strong spring enclosed within the box, and obliging the bolt, in what- 

 ever position it might be placed, to close the apertures as soon as the 

 catch was released, instead of trusting to its own weight as before. 



* I omitted to mention, in my account of the Voyage of 1819-30, that the Meteorolo- 

 gical Register was then kept in a similar manner. 



