TIDES AND CURRENTS. G81 



of fog at but a small elevation, therefore somewhat different from 

 the cirrus of the temperate zone. Instead of clouds, fogs aie 

 prevalent, now higher, now lower, and 24 hours of clear weather 

 rarely occur during the summer ; generally the sun is seen for a 

 few hours, then to disappear again behind the thick fogs. Melan- 

 choly and depressing as these fogs are, they are nevertheless 

 necessary for the general conditions of the ice ; they prevent the 

 escape of the heat of the sun's rays, and melt more ice than the 

 direct rays. 



" Parhelia and paraselen£e were often observed ; they always were 

 certain indications of coming snow-storms. A new phenomenon 

 was only observed once, when, besides the double system of 

 parhelia, two other mock suns appeared on the same altitude 

 with the real sun. 



" On the whole path which the vessel described soundings were 

 made constantly, and the depth of the sea was found to increase 

 towards the east ; on the easternmost point, 73° E. long., there 

 were 400 metres of water, and the depth steadily decreased towards 

 the west. In front of Franz- Joseph's Land there is a bank which 

 seems to reach as far as Nowaja Semlja ; beyond it the depth 

 increases again. The whole area east of Spitzbergeu rarely ex- 

 ceeds 300 metres in depth. Lieut. Hopfgarten specially con- 

 structed an instrument to fetch up dredgings, which was frequently 

 done. The deep-sea temperatures were measured with Casella's 

 minimum and maximum thermometer, and these measurements 

 were continued throughout the winter. They showed a slight 

 increase in the temperature at the bottom. The per-centage of 

 salt in the sea-water at diiferent depths was also determined. 

 Until the ship was blocked up the surface temperatures of the 

 sea were also measured. Lieut. Weyprecht thinks that, as a rule, 

 too much importance is attached to these, as the state of the 

 weather is not taken into account, and it is just that which has 

 the greatest influence upon the surface temperature ; it is quite 

 wrong to imagine the existence of currents from observations of 

 this kind." 



v.— GEODESY AND PENDULUM EXPERIMENTS TO 

 DETERMINE THE FIGURE OF THE EARTH. 



1. Parry's Pendulum Observations in Melville Island. 



These experiments were made by setting up a clock containing 

 the pendulum and observing the number of vibrations, the pres- 

 sure and temperature of the air, the arcs described, and the height 

 above the sea. 



Two clocks were used, and were the same which Captain Cook 

 took round the world. 



The pendulums were prepared by Captain Kater, being each 

 cast in one piece of solid brass^ vibrating on a knife edge of hard 

 steel on hard agate, in the form of a hollow cylinder. 



