THE EQUIPMENT 



39 



The great advantage of this method is that the ship need not 

 heave to and consume one or two hours for a sounding with line 

 and lead. A sonic depth may be made with the ship on her course 

 in from five to ten minutes. We are able to check these soundings 

 by the old-fashioned lead weight, and do so on alternate days. 



Weighing the Hydhogen-filled Balloon 

 Followed in ascent to a height of from two to seven miles in order to plot the air- 

 currents. 



In the large box on the floor are our pressure thermometers. 

 With these we have an ingenious method for checking the depths 

 recorded sonically and by wire. Besides this, the marvelous 

 instruments can tell us precisely at what distance from the sur- 

 face each of the "Nansen bottles" was reversed. 



