EFFECTS PEODUCED UPON BUILDINGS. 121 



gested, it would seem that the house might be saved from 

 much vibration. 



Ninth Experiment. — Set any of the springs in violent 

 vibration by gently shaking D E instead of the table, and 

 then suddenly cease the actuating motion. It will be 

 observed that at the moment of cessation the board and 

 the springs will have a sudden and very decided motion 

 of translation in the same direction as that in which the 

 springs were last moving, and although the springs w^ere 

 at the time" swinging through a considerable arc, all 

 motion will suddenly cease. 



This shows, that if a house is in a state of vibration 

 the strain at the foundations must be very great. 



It would not be difficult to devise other experiments 

 to illustrate other phenomena connected with the principle 

 of relative vibrational periods, but these may perhaps be 

 sufficient to show to those who have not considered this 

 matter its great importance in the construction of build- 

 ings. Perhaps the greater portion of what is here said 

 may by many be regarded as self-evident truisms hardly 

 worth the trouble of demonstration. Their importance, 

 however, seems to be so great that I hope that their 

 discussion has not been altogether out of place. 



I may remark that in the rebuilding of chimneys 

 in Yokohama the principles here enunciated were taken 

 advantage of by allowing the chimneys to pass freely 

 through the roofs without coming in contact with any of 

 the main timbers. 



In putting up buildings to resist the effects of an 

 earthquake, besides the idea of making everything strong 

 because the earthquake is strong, there are several 

 principles which, like the one just enunciated, might 

 advantageously be followed which as yet appear to have 

 received but little attention. 



