Dr. Wo LL ASTON on a Method, ^c, 1 15 



For the purpose of removing the coating of silver that sur- 

 rounds it, the wire must be steeped for a few minutes in warm 

 nitrous acid, which dissolves the silver without danger of do- 

 ing any injury to the gold. And though it might be difficult 

 in this manner to preserve any considerable length of such 

 wires, it is of little importance for any of those uses to which 

 it is likely to be applied. 



In my endeavours to make slender gold wires by the 

 method above described, the difficulty of drilling the central 

 hole in a metal so tough as fine silver, was greater than I 

 had expected, and I was induced to try whether platina might 

 not be substituted for the gold, as in that case its infusibility 

 would allow me to coat it with silver without the necessity of 

 drilling. 



Having formed a cylindrical mould i of an inch in diameter, 

 I fixed in the centre of it a platina wire previously drawn to 

 the ^ho of an inch, and then filled the mould with silver. 

 When this rod was drawn to 3^-, my platina was reduced to 

 yJL_, and by successive reduction I obtained wires of 4^^ 

 and -5 o'oQ, each excellent for applying to the eye-pieces of 

 astronomical instruments, and perhaps as fine as can be useful 

 for such purposes.* 



Since this had been the primary object that I had in view, 

 I should have thought my time ill bestowed in pursuing far- 

 ther the practical application of a method to which there seems 

 no limit, except the miperfections of the metal employed. But 

 as I found by trial the tenacity of these wires to be greater 

 than was to be expected in proportion to their substance, that 



• No very accurate observations can be made with a telescope shorter than thirty 

 inches, and at that distance x^^ of an inch subtends only one second of a degree. 



