110 



EXPERIMENTS IN AERODYNAMICS. 



Calibration of tuning-fork. 



December 12, 1S90. — G. E. Curtis, Observer. 



Temperature of tuning-fork, 18° C. 



Mean, 49.0 vibrations per second. 



The measurement of tlie strip.? showed that the clock was not " on beat," ami that two 

 successive seconds must be taken in order to get the true interval. The mean of tlie 

 measurements gave 49.9 vibrations pev second. The tuning-fork was evidently constructed 

 to give 50.0 vibrations per second, and this value was therefore adopted. The fraction of 

 a vibration can be accurately estimated to tenths ; hence the instrument, as used in these 

 observations, gave time intervals to ^^Jiy part of a second, which is sufficiently accurate for 

 tlic purpose. 



Preliminary experiments were made with the Plane-Dropper at rest indoors for the 

 pur[)Ose of testing the new contacts and the Konig registration apparatus. The pair of 

 12 X G incli planes were fastened horizontally to the falling piece. Then the observer, with 

 one hand, sets in motion the blackened strip on the Konig, and with the other, immediately 

 thereafter, presses the make-kej', which operates the release magnet of the Plane- Dropper. 

 The blackened strip containing the- registration is then passed through a solution of shellac 

 and anunonia, by which the trace is permanently set. 



The result of these preliminar}' experiments is as follows : 



Time of fall of pair of 13 x 6 inch jdanes, horizontal. 

 December 10, 1S90. — G. E. Curtis, Observer. 



