204 IOWA ACADEMY OF SCIENCE 



as vibrating chamber, with the right end of the large tube cov- 

 ered with a silvered mica membrane. The left end of the smaller 

 tube served for mouthpiece. Leaning against the large tube 

 in the foreground is seen a circular piece of silvered mica such 

 as was used for a reflecting membrane. 



SUMMARY. 



1. A new and simple method has been found for producing 

 the stroboscopic effect. 



2. The method appears to employ a general means of produc- 

 ing periodic illumination changes at a fixed point which has not 

 been hitherto used ; viz., the periodic lateral displacement of a 

 beam of light non-uniform in intensity over its cross section. 



3. A question for further investigation is : How large a 

 contribution to the changing light intensity on the stroboscopic 

 screen is due to changing curvature of the mirror? 



4. An additional experiment suggested by the stroboscopic 

 effect with the vibrating mirror is a similar experiment with a 

 vibrating convex lens, similar to that used by Bell with a 

 selenium cell. 



A NEW TONOSCOPE. 



L. E. DODD. 



While undergoing a series of voice pitch tests some three 

 years ago in the Psychological Laboratory of the State Univer- 

 sity of Iowa, the author learned that in his own individual case, 

 as in some others, there existed, according to the statement of 

 the investigator, Mr. C. J. Knock, a consistent as well as per- 

 sistent tendency to miss in a definite direction certain intervals 

 of the musical scale. The instrument used in these tests was 

 the Seashore tonoscope, 1 an indicator of absolute pitch developed 

 in some of its later stages at this University. In the particular 

 results mentioned the amount of the error was not so noticeable 

 to the ear, as the ear has its limitations, especially when it is 

 the ear of the one who is himself forming the intervals by 

 voice, but in an absolute instrument like the tonoscope even 

 very small errors can be detected. The conclusion formed by 

 the author from these results was that the musical intervals 

 concerned had been wrongly learned in childhood. 



Seashore, C. E. : Psych. Monographs, University of Iowa Studies In 

 Psychology, No. VI, June 1914, p. 1. 



