MEASUKING THE VIBKATOKY PERIODS OF TUNING-FOEKS. 53 



TA15LK IX. 



Ooiucitloucos wevo marked at 59 seconds; at 4 seconds; at 1(1.5 seconds; at 17 seconds. 

 77 — 59=18; 18-f-3=G.n=tiuie of one interval. 



Kesum6. — (1)=6.0 seconds; (2)^6.0 seconds ; (:5)=6.7 .seconds; (4)=6.3 seconds; (5)=6.5 seconds ; (r))=U. 7 sec- 

 onds; (7)=G.O: meau=6.:!l .seconds. 



(i.31Xo— :il..'i5 :U. 55+1.00=32.55 



32.55—6.31= 5. 159 

 With fork free= 5. 103 



Effect of scrape = — .004 

 Circumstances as in tirst case, except that both forks were on their resonant boxes. 



Table X. 



Coincidences were observed at 21 seconds; at 26 seconds; at 36 seconds; at 44 seconds; at 51 seconds; at 00 

 seconds. 



60 — 21=39; 39— 5=7.S^tinic of one interval. 



R^SUM]?;. — (1)=7.8 seconds; (2)^7.1 seconds; (3)=7. 6 seconds; (4).=7. 4 seconds; (5)=7.2 seconds ; inean=7.42 

 seconds. 



72.42x5= 37. 10 

 + 1.00 



38. 10 



38.10—7.42= 5.133 

 Above= 5. 159 



Kii'ect of sniiport and scrape= — . 026 



From the esperimeuts it appears that the effect of the ^vork of the fork in traciiio' its record 

 oil the smoked paper covering the cylinder, is only — .OOi of a vibration; a (iiiantity so small as to 

 be negligible, as will appear further on where we give the probable error of the mean determina- 

 tion of the numbers of vibrations per second of various forks. 



The difference in the number of vibrations given bj- the fork when vibrating on its resonant 

 box and when vibrating while screwed into the hard wooden support [H, Fig. 1), amounts to — .02G 

 less .004, or — .0J2. This result was not anticipated, and it shows how careful should experimenters 

 be in describing minutely the cliaracter of the sui)i)ort of the fork when they give the value of its 

 vibratory period. 



DcUrminatwH of the numbers of vibration per second of European forks of various standards of pitch 



[Scut me by Mr. Alexander J. Ellis, F. K. S. ] 



These forks were the si fork of 1789, of the Gha2)elle Versailles; the A fork of 1812, of the 

 Con.servatoire ; the ^4. fork of 1818, of the Theatre Feydeau; tb-e A fork of 1820, of the Tuilleries, 

 and a C fork made by Marloye of Paris. 



The determination of the pitch of these forks was made with special care, and these measures 

 may be regarded as the limits of accuracy of our method, so far as I have been able to deal with 

 it. The fractions of vibrations on the records were read otf with a microscope-micrometer, and the 

 corrections for temperature and rate of clock were carefully obtained. 



