I 2 



For the study oi intermediate depths the Fowler-net was always used. A lead of 

 3 kilogrammes was suspended from the horizontal axlc of the closing- apparatus, to prevent 

 the gauze net trom being forced up too much, during the Ietting down of the net, and thus not 

 keeping clear of the apparatus. 



The drop weights of the Fowler net were found to fall respectively at the rate of 

 0.5 metres per second (for the large weight of ió Engl. lbsj, and 1.0 metre per second (for 

 the small weight 4 Engl. lbs). Hensen's horizontal cylinder was often used. It was towed aft 

 by an ordinary rope. We slowed down when lowering it or hauling it up, but while working 

 we had a speed of from 3 to 8 miles. The depth at which this net was dragged, could be 

 controlled to some extent by the position of the tow rope and by regulating its length. 



REMARKS ON THE USE OF DEEP-SEA THERMOMETERS. 



The use of the deep-sea thermometers with which H. M. "Siboga" was equipped showed 

 some peculiarities which it may be of interest to note. While working with Negretti and Zambra 

 reversing frame, made at Copenhagen, attached to the sounding line it happened occasionally 

 that although the frame reversed correctly, the thermometer registered a temperature (2 6°. 2 C.) 

 which could not possibly be correct for the depth to which the thermometer had been lowered 

 (fully 2600 metres, and another time 4000 metres in the Ceram Sea). 



As it was absolutelv certain that the instrument had had a continually descending 

 motion from the surface to the required depth, ancl as the thermometer acted quite correctly 

 both before and after the experiment, there is but one way to account for the untimely reversing 

 of the frame. The sounding rope which was spun with a lefthanded twist being weighted with 

 leadballast ancl thermometer, together amounting to 30 kilogrammes, may on going down 

 experience a revolving motion due either to the natural untwisting of the line or to the screw- 

 like action of the twisted wire of the line in passing through the water, the water acting as 

 a nut. Xow seing that the pitch of the small screw propeller of the reversing frame is also 

 righthanded it is clear that if the frame revolves faster than the speed due to the pitch of the 

 screw the result will be that the frame wil! overtake the propeller and cause the safety pin to 

 be unscrewed and the thermometer to be untimely released. 



The screwthread of the reversing frame is righthanded. If the frame had onlv a down- 

 ward motion the loosening of the screw would be impossible on account of the waterresistance, 

 but the revolving of the frame upwards, will cause the screw in the frame to turn downwards, 

 i. e. unscrew, because the wing of the fan of the screw, furthest away trom the wire feels the 

 effect of the swinging most acutely. Xow if the influence of the revolution caused by the friction 

 of the wire, is greater than that of the friction of the descent, it is clear that the screw must 

 release the frame which consequently reverses. 



It must also be borne in mind that at the beginning of operations the rate of descent 

 comparatively slow, while the rate of revolution may be very considerable, and that die 



