SCIENTIFIC NOTES. 149 



Sir William Thompson's tide indicator is a marvel of ingenuity. 

 In it there are 13 dials or wheels which may be set so that their 

 eccentricity represents the varying effects of 1 3 of the forces acting 

 upon the tides, by passing a cord over all these wheels, and setting 

 them all in motion so as to vary their effect as the forces vary in their 

 action upon the tides. The time and height of any tide may be 

 known beforehand, subject of course to the unknown effects which 

 may be produced by the wind. In carrying out the wishes of the 

 British Association with regard to the investigation of tides he has 

 obtained many valuable results. A German professor, Dr. Schmick, 

 of Cologne, is working at tidal effects with another object in 

 view, and has written a work which is causing quite a lively discus- 

 sion on the Continent. Dr. Schmick has collected his data from all 

 possible places, north and south, and amongst them Sydney; and he 

 considers that there is unquestionable proof of an accumulating 

 secular effect upon the waters of the ocean, by which they are during 

 one long period piled up at one pole and submerge the land, and 

 then return and accumulate at the other, and that we are now in 

 the period in which the water is accumulating about the South Pole. 

 Whether the earth is subject to these changes from this or some 

 other cause is not easy to determine. But the question of molecular 

 change in substances on the earth's surface is one that can be 

 investigated niuch more satisfactorily, and some recent measures 

 taken by Colonel Clarke, of standard bars that had been sent out 

 to India, after comparison, many years since, seem he thinks at 

 least to throw doubt if not wholly to disprove the theory which has 

 been expounded, for no appreciable change was found in these bars, 

 though subject to great heat for many years. With a note of one 

 of the many curious things Sir Charles Wheatstone was kind 

 enough to show me I must close. It had occurred to him that 

 Foucault's pendulum experiment had never been carried out 

 properly, and that it would be much better to try if it would go 

 right round than assert that it would because it moved a part of 

 the way. Of course the difficulty was that the pendulum ceased 

 to swing before it had time to make the complete circle, and he set 

 himself to keep it in motion by a force which should act uniformly 

 on it, whichever way it happened to be swinging. This he did by 

 putting under it an electro-magnet, quite round, and having only 

 one pole up ; the pendulum in swinging sent a current through this 

 magnet for a moment, and it attracted the pendulum bob, so that 

 if the free pendulum would ever make a circuit by changing its 

 place of oscillation, surely this one would do it ; but no, it gradually 

 worked into the plane at right angles to the magnetic meridian, 

 and continued to swing there steadily. This was tried over and 

 over again with the same result ; and when I was in that strangely 

 furnished laboratory, Sir Charles Wheatstone was then experi- 

 menting to see if this result was brought about by the magnetism, 

 or some want of adjustment in the parts of the apparatus. 



