208 Prof. R. R. Ramsey on 



small atomic weight, may account for the periodic table, as 

 has been done by Lyon. (Phys. Rev. vol. iii. p. 232, 1914.) 



The classical method of performing the experiment is by 

 floating magnetized needles by means of corks in water. 

 I have found that small bicycle-balls floated on mercury are 

 much more convenient. (Professor Merritt used this method 

 at Cornell University in 1900.) The mercury surface lends 

 itself admirably for projection with reflected light. In pro- 

 jection it is well to focus not on the balls, but on a plane a 

 short distance above the balls, or on the focal point of the 

 concave mirror made by the depression caused by the balls. 

 The position of the ball is then shown on the screen as a 

 point of light. 



In the classical Mayer experiment the balls are fixed. 

 There is nothing to suggest how the atom may radiate. The 

 atom is dead. The motion of the atom must be imagined. 

 It is usual to imagine the needles to rotate about the centre 

 with a constant angular velocity. This is contrary to the 

 laws of planetary motion as illustrated in the solar system. 



While working with this experiment the thought came to 

 me to rotate the mercury, and thus to rotate the balls. A 

 wooden tray was made with an electrode at the centre and 

 four electrodes, one at each corner, which were connected in 

 multiple. By sending the current in at the middle electrode 

 and out at the corners one has an approximately radial 

 current flowing at right angles to the magnetic field of the 

 magnet, which plays the part of the positive nucleus in the 

 experiment. This causes the mercury to rotate and carry 

 the balls with it. 



The apparatus consists of a wooden tray, as shown in fig. 1. 

 The dimensions are 15 x 15 cm. and 2 cm. in depth. The 

 electrodes C and M are made of platinum. (It has been 

 found later that the electrodes M can be made of iron 

 without appreciably distorting the magnetic field.) A and B 

 are binding posts which are connected to the electrodes by 

 wires, shown by dotted lines, which are in grooves on the 

 under side of the box. The apparatus can be centred up by 

 placing one bicycle-ball on the mercury surface after the 

 current has been turned on through both the magnet and 

 the tray, and then shifting the tray until the ball remains 

 practically stationary at the centre of the rotating mercury. 



When two balls are placed on the rotating surface they do 

 not rotate about the centre on the same circle, as one would 

 expect from the Mayer experiment. No. 1 first rotates about 

 No. 2, and then No. 2 rotates about No. 1. Their paths 

 resembling rotating ellipses. With three balls the motion is 



