Intelligence and Miscellaneous Articles. 287 



with each touch of the platinum point. The clock through this 

 mercury connection was placed in the circuit of the primary coil of 

 an inductorium, the current of which was given by a single voltaic 

 cell. The tuning-fork, with one of its prougs armed with a light 

 style of thin elastic copper-foil, was screwed to a board with a hinge 

 w T hich, with a screw-stop suitably placed, allowed of its being 

 iuclined so that the style was just in contact with a smoked surface 

 of paper wound on a rotating cylinder. The secondary circuit of 

 the induction-coil included the fork and cylinder. In the experi- 

 ment the fork w 7 as raised on the hinge, set vibrating by a bow, and 

 then depressed again, so that the style should write out its vibra- 

 tion on the smoked surface ; at each second, as the platinum-pointed 

 pendulum left the mercury, the primary circuit was completed and 

 an induced current caused a spark from the point of the style, 

 which made a single minute circular white spot on the blackened 

 surface. The determination of the vibration-period of the fork is 

 obviously given by counting the number of waves in the trace, and 

 measuring the fraction of a wave with a microscope-micrometer. 

 It was found to be essential to accuracy that the induction discharge 

 should give a single spark only, and that the spot made by it should 

 bisect the trace of the fork. A series of experiments with discharges, 

 obtained on a rapidly rotating surface of blackened paper with cur- 

 rents of various strengths, showed that the discharge is ordinarily 

 complex, and consists of a shower of sparks producing a large 

 number of spark-holes on the paper. The proper conditions to be 

 fulfilled to give the single spark-hole with a given induction-coil 

 can only be obtained by a series of experiments varying the strength 

 of the primary current and the area of the condenser in the secon- 

 dary. In the experiments described the primary coil was 150 feet 

 in length, the secondary 8 miles, and a condenser of plates of glass 

 with tinfoil with 50 square inches of area was employed. 



With the instrument which has been described a number of 

 separate investigations were made. The first had to do with the 

 question of the influence of varying amplitude on the time of vibra- 

 tion. With amplitudes varying in one case from 1*19 to 0*59 

 millim., in another from 239 to 0*61, and a third from 2*07 to 

 0*78, no variation in vibration-period greater than 0*5 of a vibra- 

 tion was noted. In a second series of experiments the effect of 

 temperature was considered, and the result established with six 

 Kcenig forks with Ut 2 and Tit. as extremes, that for all forks of 

 the same steel and shape the effect of change of temperature was 

 the same. A change of 1° E. produced a change of vibration- 

 period of -zYhzT P art - ^- n an °ther series of experiments the law 

 of the running down in the amplitude of a fork's vibration, and 

 in another the numbers of vibrations per second of some European 

 forks of various standards of pitch, were determined. In the latter 

 determinations the probable errors in one of the mean cases was 

 estimated to be + *0053 of a vibration ; in another + *004 of a 

 vibration. 



Professor Mayer discusses further the use of the apparatus de- 

 scribed as a chronoscope, and gives the results of some experiments 



