4:86 Scientific Intelligence. 



and measuring' the fraction of a wave with a microscope-microme 

 ter. 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 black- 

 ened paper with currents 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 experi- 

 ments varying the strength of the primary current and the area 

 of the condenser in the secondary. In the experiments described 

 the primary coil was 150 feet in length, the secondary 8 miles, 

 and a condenser of plates of glass with tin foil with 50 square 

 inches of area were 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 

 vibration. With amplitudes varying in one case from l-lQ" 1111 to 

 0-59, in another from 2-39 to 0-61, and a third from 2*07 to 0'78, 

 no variation in vibration-period greater than - 05 of a vibration 

 was noted. In a second series of experiments the effect of tem- 

 perature was considered, and the result established with six 

 Koenig forks with Ut 3 and Ut 5 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° F. produced a change of vibration- 

 period of a 1 1 6 1 part. In another 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 Euro- 

 pean 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 

 described as a chronoscope, and gives the results of some experi- 

 ments with it on the velocity of fowling-piece shot of various 

 sizes with various charges of powder. The degree of uniformity 

 of rate of rotation of the cylinder is shown to be immaterial, and 

 further it is shown that no correction is needed for the weight of 

 the tracing style nor for its scrape on the paper. With an A fork 

 with 440 vibrations per second, it is stated that the number of 

 vibrations can be determined by this method to at least T -^-g- of a 

 vibration, and the time record consequently to jx.Vdt °f a secon .d. 



II. Geology and Natural History. 



1. Fourth Annual Kei^ort of the XT. S. Geological Survey. 

 1882-'83; by J. W. Powell, Director. 474 pp., royal octavo, 

 Washington, 1884. — This fourth report of the U. S. Geological 

 Survey, recently distributed, contains, like its predecessors, large 



