%8$ Intelligence and Miscellaneous Articles, 



density as water. This liquid is a mixture in suitable pro- 

 portions of nitrobenzole and oil of turpentine. The very fine 

 bubbles of emulsion pass along the axis of the jet, of which they 

 take the exact velocity, as I have ascertained by modifying the 

 density of the liquid ; within pretty wide limits experiment 

 shows a velocity independent of this density. This velocity is 

 occasioned as follows. 



The image of the jet, and therefore that of the bubbles, is formed 

 on a photographic plate, which, by means of a suitable mechanism, 

 is made to move at right angles to the trajectory of the jet. When 

 the liquid begins to flow out the plate is exposed, and thus the 

 sensitive plate receives the image of the jet during its passage. 



The developed plate shows then one or more lines according as 

 one or more bubbles have passed during the course of the plate. 

 These lines are slanting ; the direction of each is made up of two 

 rectangular motions, that of the plate and that of the bubble. 

 The velocity of the plate is determined by the vibrations of a 

 tuning-fork, and the exact direction of the motion of the photo- 

 graphic plate is marked by a dotted line. The angle which one of 

 the slanting lines of the photographic plate makes is measured ; from 

 this angle we easily deduce the velocity of the bubble, and hence 

 that portion of the jet which is being investigated. 



I have applied this method to the measurement of the velocity 

 of efflux through an orifice in a thin plate 5'90 millim. in diameter 

 under pressures varying from 0*15 metre to 0-30 metre of water. 

 These experiments have been at first intentionally limited to such 

 similar pressures, in order that we could settle by the constancy of 

 the results the real accuracy of the method. With an imperfect 

 apparatus, the mean error has remained below y^.. 



I intend to investigate in this way, but under considerably 

 different pressures, the efflux of different liquids, and particularly 

 of viscous ones.— Comjptes Bendus, Jan. 18, 1886. 



A METHOD OF PRECISELY MEASURING THE VIBRATORY PERIODS 

 OF TUNING-FORKS. BY PROF. A. M. MAYER. 



The third volume of the Memoirs of the National Academy of 

 Sciences contains a paper by Professor A. M. Mayer, embodying the 

 results of a research recently carried on by him with funds from 

 the Bache endowment. This research has as its object the elabo- 

 ration of a method for measuring accurately the times of vibration 

 of tuning-forks, and the determination of the laws of their vibra- 

 tions with reference to the use of the tuning-fork as a chronoscope. 

 The method employed was briefly to make a clock flash, at each 

 second, a spark of induced electricity on a trace made by a style 

 attached to the prong of the vibrating fork. To accomplish this 

 the pendulum of the clock was armed with a triangular piece of 

 platinum-foil, which each second cut through a globule of mercury 

 contained in a small iron cup. To ensure the best results fresh 

 mercury was taken with each experiment, and the height of the 

 mercury was adjusted by a screw-collar in such a way as to make 

 the globule as nearly as possible rigid and free from vibrations 



