Jan. 20, 1 881 J 



NATURE 



281 



ELASTICITY OF WIRES ^ 



T 



HE experiments described in this paper form a continuation 

 of experiments undertaken in connection with the work of 

 the Committee of the British Association for commencing secular 

 experiments on the elasticity of wires. 



Long-continued application of stretching force increases to a 

 very great extent the ten-.ile strength of soft iron wire. Thus in 

 experiments described to the British Association in 1879 (see 

 Report of the Committee just referred to), a particular very soft 

 iron wire was shown to have a breaking; weight 10 p.c. higher if 

 the weight necessary to break it is applied half a pound at a time 

 per day, than it has if the breaking weight is applied half a pound 

 at a time at intervals of say two minutes. It was found also that 

 this wire, quickly broken, extends before breaking by as much 

 as 25 p.c. of its original length ; whereas if thi application of the 

 stress is very slow, the extension is not more than 5 or 6, or 

 perhaps 8 p.c. \ urther experiments have been undertaken on 

 this subject, and are still in progress. 



Using a continuous arrangement for applying the stretching 

 weight and employing some very soft iron wire which had been 

 specially prepared, and which was used in former experiments, 

 the greatest weight which could be rapidly put on the wire 

 without breaking it was determined. It was found that with a 

 weight of 41 lbs. gradually applied in (>\ minutes the wire 

 stretched by 24'4 p.c. of its original length, and broke 18 

 minutes after the weight was put on. With the same weight, 

 41 lbs., applied in 64 minutes, the wire stretched 22' i p.c. and 

 broke in 24 minutes. With 41 lbs., hosvever, applied in 7J 

 minutes, the wire stretched iS p.c, and did not break. This 

 weight, therefore, appeared to be just as much as the wire 

 would bear with this method of applying the weight. Accord- 

 ingly it was applied to a great number of wires for different 

 lengths of time for the purpose of hardening them, and arrange- 

 ments have been made for keeping a number of wires for very 

 long times with this stretching force applied to them. The 

 amount of extension produced by the application of the hardening 

 stress was observed in each case. 



After the hardening stress had been applied for a certain time 

 the additional weight necessary to break the wire was determined, 

 and also the additional elongation before breaking, which was 

 in all cases almost insensible. The wires seemed permanently set 

 in about forty minutes from the time when the hardenmg stress 

 was appHed. They did not alter in length till just before they 

 broke, when they generally stretched I or 2 millimetres on a 

 length of about 1,800 mm. The following table shows some of 

 the results out of a great many that have already been obtained. 



Curves have also been obtained and were exhibited to the 

 Section showing the extension with gradually applied weights 

 both of a number of wires and of the different parts of the same 

 wire ; also curves showing the extension at different intervals of 

 time from the beginning of an experiment in which the wire is 

 running down under a weight sufficient to break it finally. 



The author acknowledged the great assistance that he had 

 received from Mr. A. C. Crawford and other students the in 

 Physical Laboratory of the University of Glasgow. 



Similar experiments are in progress on wires of copper and 

 tin, and it is intended to test gold wire very soon, as it will 

 probably give interesting results, and results very different from 

 those given by soft iron wires. 



' Strength and Elasticity of Soft Iron Wires. Abstract of a Paper read at 

 the British Association, by J. T. Bottomley, M.A., F.R.S.E. 



SPECTROSCOPIC NOTES, 1879-80. 



D 



OUBLE Reversal 0/ Lines in Chromosphere Spectrum. — The 

 magnesium lines of the b group, and the two D-lines of 

 sodium have been seen several times (first on June 5, 1S80) doubly- 

 reversed in the spectrum at the ba.se of a prominence. 



A bright line first appears in the centre of the widened dark 

 lines ; then this bright line grows wider and hazy at the edge, 

 and a thin dark line appears in its centre, as shown in the figure. 

 The phenomenon la-ts usually from ten minutes to an hour. It 

 is evidently the exact correlative of the double re\'ersal of the 

 blight sodium lines, observable in the flame of a Bunsen burner 

 or alcohol lamp under certain circumstances when the quantity 

 and temperature of the sodium vapour in the flame are greatly 

 increased . 



The Hliiies in the Chromosphere and Sun-spot Spectra. — In 

 1872 I found the H- and K-lines to be reversed in the spectra 

 of prominences and sun-spots, as observed at Sherman, Sooo 

 feet above the sea. Until recently I have not been able to 

 verify the oI)servation, except for a moment during the eclipse of 

 1878. During the past summer, however, I have succeeded in 

 seeing them again, and with suitable precautions as to shade- 

 glass, adjustment of slit to true focal plane for these special 

 rays, and exclusion of extraneous light, I have no further diih- 

 culty with the ob-ervation. The spectroscope employed has 

 collimator and view-telescope each of \\ inches aperture, and 

 about 13 inches focal length, and a speculum-metal Ruther- 

 furd grating with 17,300 lines to the inch. A shade of cobalt- 

 blue glass greatly aids the observation. The solar image is I J 

 inches in diameter. 



In the spectrum of the chromosphere, H and K are both 

 ahuays reversed. I have never failed to see them both when 

 circumstances were such that /;, the nearest of the hydrogen 

 lines, could be seen. 



Furthermore, H, in the chromosphere spectrum, is ahuays 

 double : that is, a fine bright line ^always accompanies the prin- 

 cipal line, about one division of Angstrom's scale below. The 

 principal line seems to be exactly central in the wide dark shade, 

 the other is well within the nebulosity. K on the other hand 

 shows no signs of duplicity. 



In the spectrum of a sun-spot H and K are also, both of them, 

 generally, though not always, reversed ; and the reversal is not 

 confined to the spot, but covers often an area many times larger 

 in its neighbourhood. 



In the spit spectrum, however, H has never yet been seen 

 double. The companion line of H is therefore probably due to 

 some other substance than that which produces H and K ; a 

 substance prominent in the chromosphere, but not specially so in 

 the neighbourhood of spots. In view of the recent observations 

 of Vogel, Draper, and Huggins, it is natural to think that 

 hydrogen is probably the element concerned. If so, it may be 

 expected that H will be found doubled in the spectrum of a spot 

 which reverses the hydrogen line /;. I have not yet been able to 

 test it in this way, as /; is rarely seen reversed, though C and F 

 occur pretty frequently, 



[Note. — An observation made since my paper was written 

 leads me to modify this opinion, that the companion of H is 

 due to hydrogen, and satisfies me that in all probability both 

 H and K must themselves be hydrogen-lines. At 11 A. M. on 

 October 7, a bright horn appeared on the S.E. limb of the sun. 

 When first seen it was about 3' or 4' in elevation, but it rapidly 

 stretched up, and before noon reached a measured altitude of 

 over 13' (350,000 miles +) above the sun's limb. It faded away 

 and disafjpeared about 12.30. It was brightest about 11.30 

 with an altitude of about 8' and at this time both H and K were 

 distinctly, and for them, brilliantly reversed in it clear to the 

 summit. H was not double in it to any notable elevation, 

 though the companion of H was visible at the base of the 

 prominence. The H- and K-Iines also showed evidence of 

 violent cyclonic action, just as C did. /; was only faintly visible 

 in the prominence ; F and the line near G were of course strong. 

 But no other lines, either of sodium, magnesium, or anything 

 else, could be traced more than a very few seconds of arc above 

 the sun's limb. I am not able to say how long the H-lines 

 continued visible, or to what elevation they extended afterwards, 

 as I returned to the C-line to watch the termination of the erup- 

 tion. If I remember rightly, this eruption reached a higher 

 elevation than any before observed. There was (and is to-day) 

 nothing on the sun's limb visible with the telescope which would 

 account for it. — Princeton, October S.] 



