334 REPORT— 1893. 



upper parts. If one considers these circumstances it does not appear 

 improbable tliat the pendnlam might be affected by temperature in a 

 different way from the level on the other side. 



The large motion of the pendulum is felt as a great drawback when 

 it is necessary to give it a high degree of sensitiveness, because it re- 

 quires a constant watching of the light-point in order to make the 

 necessary corrections before it leaves the paper. But another difficulty 

 arises, because when a strong motion of the pillar takes place in the 

 N. S. direction it is only natural to suppose a similar motion to take 

 place in the E. W. direction, which must cause a perpetual change in the 

 scale value. 



During the observations at Strassburg the period of the pendulum 

 was observed every now and then, and as it had not varied much at 

 first, observations were taken at longer intervals afterwards. On 

 May 10, however, when a new determination was made by Professor 

 Becker with the chronograph, it was found that the period, which had 

 been 12*4 seconds (one-half swing) before, had risen to 17'4> seconds, 

 which indicates that either the pillar had been tilted considerably from 

 the west to the east, or that a sudden displacement of the pendulum must 

 have taken place, perhaps during one of the earthquake-shocks, the effects 

 of which were mentioned above. 



Should other observers try the horizontal pendulum they may gather 

 from the above that it is almost necessary to use a double pendulum for 

 observing both components of the deflections, and that arrangements 

 should be made to determine the period of oscillation at short intervals 

 whenever a strong motion of the zero-point is indicated. 



Dnring the winter a curious fact was communicated to me by Pro- 

 fessor Kortazzi. In trying to explain the motion of the zero-point he 

 had placed a hygrograph in the cellar with the pendulum, and found 

 that the pendulum was decidedly influenced by the relative moisture of 

 the air in the cellar, for the diagrams were much like each other. In a 

 letter to me he expressed the following opinion. The column which 

 carried the pendulum had been piled up of large loose stones without 

 mortar or cement in order to be able to begin the observations without 

 the loss of time caused by the drying process. The ground of the cellar 

 being perfectly dry, it appears that the stone behaved like a sponge, 

 drawing in the moisture contained in the air more or less, and thereby 

 causing a change in the inclination of the instrument. I have lately 

 heard from Professor Kortazzi that the effect of moisture disappeared 

 almost entirely when the openings through which the cellar communi- 

 cated with others were closed, and the pillar was covered with a water- 

 proof material. 



It is evident that if this cause has a considerable effect at Nicolaiew, 

 it could only have been of secondary importance at the other stations. 

 At Wilhelmshaven, for instance, the relative moisture of the air was 

 probably always 100 per cent. It is necessary, however, to consider this 

 agent also, and to take the necessary precautions in order either to avoid 

 or to eliminate its effect as much as possible in the final results. A dry 

 and wet bulb thermometer have therefore been placed in the cellar at 

 Strassburg, and are read twice every day.' 



' It may be useful to mention that observations with two horizontal pendulums, 

 exactly like the one used by myself, are now being made by Prof, Lewitzky at 

 Charkow. 



