78 Mr. H. Tomlinson on the Effect of Heating and 



Messrs. Johnson and Nephew, and was specially prepared 

 and annealed for the author by these makers ; it was again 

 annealed by the author himself in the following manner : — 

 The piece of iron wire, together with several others, was 

 placed in an iron tube about 180 centim. long ; the tube and 

 its contents were then heated, in one of Fletcher's new tube- 

 furnaces, to 1000° C. This high temperature was preserved 

 for several hours, and the wires were then allowed to cool 

 slowly in the furnace. The above operations were repeated on 

 three different days, so that eventually the wire was probably 

 annealed as well as it could be by the ordinary method. In 

 order to avoid any appreciable effect from the earth's mag- 

 netic force, the furnace was placed in a direction at right 

 angles to the magnetic meridian. After the annealing the 

 wire, which was about 120 centim. long and 1 millira. in dia- 

 meter, was wrapped round wdth strips of paper, and wound 

 double in a coil 5 centim. in diameter and 12 centim. in length. 

 It was then placed in an air-chamber consisting of two co-axial 

 copper cylinders (see fig.) connected at their extremities, and 

 enclosing between them an annular space filled with water. 

 The whole arrangement is sufficiently shown in the figure. 



## siz* 



Gas 



Battery 



In this figure O O are two clamps grooved so as to receive 

 the ends of the iron wire a 1 *, the clamps themselves being 

 soldered to stout copper connecting-rods ; a German-silver 

 wire, ?/, is similarly connected, and placed in a glass vessel. 



* If the grooves, and the ends of the wire which fit into them, be well 

 cleaned, clamping serves quite as well, for the purpose of connexion, as 

 soldering, and is more convenient. 



