534 



reality the defleetioiis are not proportional to the square of the 

 length of the string, as would be the case in an absolutely homo- 

 geneous field. This is caused by the central weaker part of the 

 field, which infiuence increases if the string is shorter. 



We should try to minimise the influence of the bore. We have 

 already considered one way of doing it, i.e. to make the bore 

 as narrow as possible. It is however difficult to make the bore 



