

On the Bearing of Recent Observations upon Solar Physics. 447 



in the sides of the rectangular space in the base-board; they 

 have fixed to them two small vertical plates or armatures of soft 

 iron, the lower edge of each of which has a small notch filed in 

 it which fits and presses upon the iron wire ; and when the appa- 

 ratus is going to be used, a permanent bar-magnet L is placed 

 with its poles resting upon the upper ends of these armatures. 

 The iron wire employed is usually about 4 millims. in diameter, 

 and the apparatus is sufficiently powerful to readily elongate iron 

 wire of that size. M is a rectangular or T-piece of wrought iron 

 of the form and dimensions indicated by the figures ; it is move- 

 able, and may be readily taken off the end of the base-board by 

 removing the screws N (of which there is one on each side) . The 

 ends of the wires require to be held very securely during the 

 strain ; this is perfectly effected by having in D and in M two 

 steel screws each 6 millims. diameter. The level of the top sur- 

 face of the small brass rollers is slightly above that of the ends 

 of the iron wire. 



By means of this apparatus I have repeatedly verified the fact 

 that a magnetized soft iron wire, during the act of being stretched 

 (either with temporary or permanent elongation), increases in mag- 

 netism, and produces a current of electricity in the coil of wire 

 G in a contrary direction to that of the hands of a watch, i. e. in 



the direction of r^\ , when we are looking at its south pole, cor- 



responding to that of the north pole of the magnet above it. 

 With a galvanometer of moderate sensitiveness, the amount of 

 deflection of the needles was generally about 14 degrees on one 

 side by a single stretch of the wire, or 17 degrees on each side by 

 repeated synchronous stretches. No deflections were obtained 

 by stretching thick wires of zinc or copper. The apparatus was 

 placed in a direction of east and west during the experiments. 



The results obtained with iron agree with the fact discovered 

 by Mr. Joule, that straining an iron wire lowers its temperature, 

 and also with the well-known fact that lowering the temperature 

 of a piece of iron increases its magnetic capacity. 



LV. On the Bearing of Recent Observations upon Solar Physics. 

 By G. Johnstone Stoney, M.A., F.R.S. 3 §-c* 



97. T J^HE main difficulty in dealing with solar and stellar 



-1- physics arises out of the scantiness and fragmentary 



character of our data. This makes the inquiry a very treacherous 



one — so much so, that some of the most eminent men have gone 



* Communicated bv the Author. 



