hf drawing extremely Jine Tfires, 117 



metals within moderate limits, continued also to add something 



to the tenacity of platina even as far as -o ' ' of an inch, which 

 *' 1 0,000 ' 



supported ij- grain before it broke; but the wire on which 

 these experiments were made began then to be impaired by 

 repetition of the operation: so that although I afterwards 



obtained portions of it, as small as — ^ — of an inch in diameter, 



it was in many places interrupted, and I could place no reli- 

 ance upon any trials of its tenacity. 



There are some little circumstances in the management of 

 these fine wires, which it may be of advantage to describe for 

 the assistance of those who would apply them to any useful 

 purpose. When the diameter is not less than t^Vo or toVo 

 of an inch, the difficulty of seeing and applying them in short 

 pieces is not considerable; but when their diameter is farther 

 reduced, and their length as much as an inch or more, the 

 slightest current of air is sufficient to defeat all attempts to 

 lay hold of an object so difficult to see, and so impossible to 

 feel. It is therefore necessary to retain a part of the silver 

 coating at each extremity, which, at the same time that it 

 assists in finding the end, also serves to stretch the wire with 

 a certain moderate tension, and affords the means of attaching 

 it in any required position. 



The method that I have found most convenient is to bend a 

 portion of the coated wire into the shape of the letter U, with 

 small hooks at its upper extremities. In this form it will con- 

 veniently hang upon a wire of gold or of platina, with the 

 lowest part immersed in nitrous acid, till the coating of silver 

 is removed from that part. It may then, without difficulty, be 



