On Gravimeters. 533 



I could not pinch it tight enough to hold. Subsequent examination 

 showed no sign upon the gold wire. 



This proves conclusively that, under these circumstances, the pinch 

 of a round wire is an insecure hold against torsion.* 



I cannot but regret this result, for the sake of the exquisite work- 

 manship ; but there is no help for it, the wires must be held in some 

 other way before anything can be done to test the instrument as a 

 gravimeter. I find, for instance, that a slight flattening of the wire 

 meets the slipping difficulty perfectly ; but a flattened wire strains 

 (i.e., takes up a twisted or strained condition) very readily, and it is 

 doubtful whether any alteration of the cylindrical form, even for a 

 very small part of the length, can be permitted without risk. 



My examination having reached this stage, I found it necessary to 

 decide whether to stop here or run some risk of injuring the apparent 

 perfection of the instrument, in the endeavour to obtain the first 

 requisite, a firm hold of the ends of the torsion wire. I defer, for the 



* I have since tried a steel wire pinched between lead sheets in a vice. No pinch 

 seems sufficient to prevent the slipping, if the wire is straight, but a slight crook 

 suffices. 



