498 Messrs. Stewart and Loewy on the true [June 17, 



Table II. {continued), 





Betwt 



jen 2 and 3 inches. 



Between 1 anc 



2 inches. 



Below 1 inch. 



No. of 

 experi- 

 ment. 





















Temp. 



Pres- 

 sure. 



Vibra- 

 tions. 



Temp. 



Pres- 

 sure. 



Vibra- 

 tions. 



Temp. 



Pres- 

 sure. 



Vibra- 

 tions. 





o 



inches. 







inch. 









62-76 



inch. 





I. 



51-50 



2 *373 



86023*23 



6o° 97 



I- 393 



86023-35 



0-472 



86023-26 



II. 



48-93 



2-462 



86023-09 



59'47 



1-416 



86023-24 



60-85 



0-431 



86023-47 



III. 



55*55 



2-50! 



86023-05 



58-32 



1-411 



86023-04 



60-79 



0-444 



86023-60 



IV. 



5476 



2-389 



8602321 



61*15 



i-43o 



86023-45 



61-57 



0-451 



86023-74 



V. 



5^38 



2-417 



86023-08 



60-83 



1-471 



86023-65 



62-36 



0-425 



86023-79 



VI. 



54^4 



2-451 



86023-23 



57-58 



1-319 



86023-17 



60-77 



0-389 



86023-31 



VII. 















49-72 



0-427 



86023-55 















Table III. Mean results of Pressure-experiments. 





Mean 



Mean number 





Mean 



Mean number 





pressure. 



of vibrations 





pressure. 



of vibrations 





inches. 



per diem. 





inches. 



per diem. 



I. 



0-434 





VII. 



7-486 





II. 



1-407 





VIII. 







III. 



2-432 





IX. 



14-569 





IV. 



3*!74 



86022-87 



X. 







V. 



4-310 



86022-58 



XI. 







VI. 







XII. 



29-952 



86013-85 



while Table III. contains the resulting means for the different sets, as 

 specified in paragraph 4. 



The experiments made at a full atmospheric pressure are the same as 

 those given previously in connexion with the temperature-experiments, 

 but they are here repeated for the sake of comparison. Their mean 

 temperature being 47°' 16, the whole of the other experiments has been 

 reduced to the same temperature by means of the coefficient adopted in 

 accordance with our preceding statement. 



The results as given in Table III. do not require any special remarks. 

 It will be seen that the resistance of the air to the motion of a pendu- 

 lum, as measured by the number of its vibrations, increases very slowly up 

 to 7 or 8 inches of pressure ; a more energetic action is exerted up to 

 about 20 inches, and after that point the resistance increases very slowly 

 up to the full atmospheric pressure. 



This behaviour is represented in a more impressive manner on the ac- 

 companying curves. One of them, marked A, shows simply the result- 

 ing number of vibrations at the given pressures, which latter form the 

 abscissae, while the former are the ordinates. The second curve, B, is 

 derived from A, by assuming the whole correction necessary to reduce the 

 pendulum observations made in air to a vacuum as unity, and expressing 

 the correction for intermediate pressures as fractions. The ordinate 

 representing unity has been divided into forty parts, each representing 

 0*025, enabling us to represent the correction to three decimals with 

 great precision. 



