Chemistry and Physics. 391 



obtained that this resistance with each increase of frequency 

 behaved more like a solid resistance. The alternator was altered 

 until the very high frequency of 120,000 cycles per second was 

 obtained. The alternator was first driven by a figure of eight 

 drive consisting of two bicycle wheels, one fixed direct to the 

 motor shaft as the driving wheel, the other acting as a tension 

 pulley to balance the pull on the alternator spindle. A surpris- 

 ing amount of power was required to drive the bicycle wheel at 

 high speeds even without the inductor, and the author computes 

 that the air friction on a single bicycle wheel running at 1200 

 revolutions per minute, or at a rim velocity of about 85^ miles 

 per hour, required an expenditure of energy at the rate of about 

 200 watts ; so that a cyclist to attain this speed would have to 

 develop over one-half horse power to overcome the air friction 

 on his wheels alone. The bicycle wheels were replaced by two 

 phosphor-bronze discs, both being made drivers. The author 

 describes his difficulties with belts. A cotton cord three-six- 

 teenths of an inch in diameter gave the best results. In spite of 

 every care all attempts to run the inductor at 1000 revolutions 

 per second failed from the axis of inertia of the inductor not 

 coinciding with its mechanical axis. If these axes were parallel 

 and l mm apart, the pressure at 1000 revolutions per second on the 

 two bearings would amount to 0*8 metric ton, which would be 

 prohibitive on such small bearings. The inductor consisted of 

 laminated toothed discs of iron which revolved between two pole 

 tips provided with coils. A current of 0'1 ampere was obtained at 

 a frequency of 120,000 per second. As an illustration of this 

 high frequency the author remarks that in plotting curves for 

 ordinary frequencies of 50 to 100 cycles per second the scale 

 often adopted is 10 inches for 100 cycles. If it were attempted 

 to plot a curve up to 120,000 cycles per second the paper would 

 require to be nearly one-fifth of a mile long. — Phil. Mag., March, 

 1905, pp. 299, 309. j. T. 



7. Deviation during Free Fall. — It is still a question whether 

 a southerly deviation of a freely falling body has ever been 

 detected. De Sparre asserts that the formulae usually given for 

 easterly and southerly deviation during free fall are erroneous ; 

 for the variation in centrifugal force and the magnitude and 

 direction of the weight are generally neglected. He gives mathe- 

 matical expressions for the southerly deviation, according as the 

 fall takes place in a well or from a tower. In any case the 

 southerly deviation is too small for measurement, being less than 

 0-l mm for a fall of l km . — Comptes Pendus, cxl, Jan., 1905, pp. 

 33-35. j. t. 



8. Polarized Pontgen Radiation; by Charles G. Barkla. 

 (Abstract of a paper read before the Royal Society of London, 

 Feb. 16, 1905.) — Experiments on secondary radiation from gases 

 and light solids subject to X-rays showed that the character of 

 this radiation differs only very slightly from that of the radiation 

 producing it, and that the energy of this radiation is proportional 



