174 M. G. E. Svedelius on the Changes in the Length and 



say a few words in regard to the instruments, materials, and 

 methods used in my experiments. 



The material for observation has partly consisted of cold- 

 drawn wire from Bofors iron-works containing from 0"9 

 per cent, to O'l per cent, of carbon, with a diameter of 



3 millim., and partly of hot-rolled wire from Sandviken 

 iron-works containing from 1*0 per cent, to O'l per cent, of 

 carbon, with a diameter varying between 5*4 millim. and 

 5*6 millim. 



All the linear measurements have been taken with a dila- 

 tometer which in principle corresponds to the dilatometer 

 devised by Prof. Angstrom*. The iron or steel bar about 



4 centim. long, whose changes in length were to be observed, 

 was fitted in between the two ends of two rather long hori- 

 zontal arms of porcelain A and B, one of which was fixed and 

 the other movable around a vertical axis. The arms, which were 

 drawn towards each other by a weak spiral spring C, pressed 

 against the rod D (see diagram p. 175). The opposite ends of 

 the arms were allowed to move a mirror K fastened to a torsion- 

 wire H, H. The rod was heated by a Muenches patent burner, 

 and its temperature was measured by a thermoelectric couple 

 of platinum and platinum-rhodium alloy and a mirror-gal- 

 vanometer. The readings of the dilatometer and galvanometer 

 were noted, either each by itself or both at a time, parily by 

 telescopic observations and partly by photographic recordings. 

 In the latter case, pencils of light reflected from the mirrors 

 of the dilatometer and galvanometer fell upon a strip of paper 

 sensitive to light, which was moved through a dark box with 

 uniform rapidity. The photographic image thus formed con^ 

 sequently described curves whose ordinates reproduced without 

 interruption every change of length and temperature in 

 the rods. 



Suitable allowances have been made for the errors of the 

 dilatometer due to the heating of the arms. Reproductions 

 of the longitudinal curves recorded by photography are 

 annexed to this paper, but they are not corrected, and are 

 therefore not suited for absolute measurements. They give, 

 however, a rather good idea of the general expansion and 

 contraction of the bar. 



Experimental Results. — The curves reproduced in figs. 1-12 

 are true copies of longitudinal curves of different iron and 

 steel rods recorded by photography. 



The rods have, where not otherwise stated, before each ex- 

 periment been heated to a bright red heat, and have then been 

 allowed to cool slowly. 



* Bihang till Vet. Akad. Handl. xiii. (1887) Afd. i. No. 6. 



