308 



Transmission of Waves by a Grating. 



accuracy was secured by counting only about half this 

 number, owing to the occurrence of ripples due to accidental 

 tremors, which interfered sensibly when the amplitude had 

 become very small. The intervals of time measured in 

 successive experiments under the same conditions were found 

 to agree within 0*2 sec, so that the period of oscillation 

 could be inferred with an error oE not more than 0*002 sec. 



The results are shown in the annexed table. The first 

 column gives the depth of the water beneath the point of the 

 hook gauge. The second column shows the period as 

 observed when there is no obstacle, and the third as calculated 

 from the formula ((5). The fifth and sixth columns show the 

 observed and calculated periods when a cylindrical obstacle 

 of tha diameter indicated is introduced, the theoretical period 

 being based on the formula (21), as explained. The last two 

 columns show the observed and calculated increase in the 

 period, due to the obstacle, in the various cases. 



I 



Period when 









Increase in 



Depth 



no cylinder present. 



Diameter 



Period. 



period. 



or 



water. 







of 

 Cylinder. 























Obs. 



Oalc. 



in8. 



Obs. 



Calc. 



Obs. 



Calc. 



ins. 















73 



2-324 



2-313 



45 



2-489 



2-479 



•165 



•166 



»> 



2-324 



2-313 



3-45 



2-413 



2-401 



•089 



•088 





2324 



2-313 



2-21 



2-358 



2-346 



•034 



•033 



,, 



2-324 



2-313 



1-59 



2-338 



2-329 



•014 



•016 



8 



2-210 



2-221 



4-5 



2-364 



2-380 



•154 



•159 



I* 



2-224 



2-221 



3-45 



2-304 



2-304 



•080 



•083 



,, 



2215 



2-221 



2-21 



2-245 



2-252 



•030 



•031 



., 



2-212 



2-221 



1-59 



2-226 



2-237 



•014 



•016 



84 



2-167 



2-173 



4-5 



2-322 



2-328 



•155 



•155 



j) 



2-167 



2-173 



3-45 



2-249 



2-254 



•082 



•081 



j, 



2-167 



2173 



2-21 



2-198 



2-204 



•031 



•031 



, 



2-168 



2-173 



1-59 



2-182 



2-189 



•014 



•016 



9 



2112 



2-108 



4-5 



2-258 



2-257 



•146 



•149 



>> 



2-112 



2-108 



3-45 



2-192 



2-187 



•080 



•079 



j> 



2-112 



2-108 



2-21 



2-142 



2-138 



•030 



•030 





2-101 



2-108 



1-59 



2-115 



2123 



•014 



•015 



9 ! 4 



2-062 



2-070 



4-5 



2-211 



2-215 



•149 



•145 





2-063 



2-070 



3-45 



2-138 



2-146 



•075 



•076 



" 



2-062 



2-070 



221 



2-088 



2-099 



•026 



•029 





2-062 



2-070 



1-59 



2-075 



2-084 



•013 



•014 



A slight and variable error in level in the bed of the tank 

 could not be avoided, and the depth measured at the position 

 of the hook-gauge does not therefore represent quite accurately 



