PHYSICS, PROGRESS OF, IN 1801. 



attainable cold is about 2-Vi , IN above abeo- 

 lull- /ero. I'rc'f. 1'ictd olitaiiis his low tem- 

 perature- liy c\ap<iralion in three stages. Kir-l, 

 u mixture of liquefied Milpliuroiis acid and 

 carbonic acid i;a-rs produces by its evaporation 

 a tcin|icraturc of 80. At this temperature 

 nit roil-* o\idc cun bo liquefied, and tliis by its 

 evaporation product's a temperature of 155, at 

 which ordinary air is liqueiiable. The lii|ueli.-d 

 air. in its turn, by its vapori/.atioii brings the 

 temperature below 200. 



Light (For various experiments bearing on 

 the electro-magnetic theory of light, see under 

 irieity " and " .Magnet ism "). Aln n-nlinn. 

 Locsvy and Puiscux ("Comptcs Kcndus," March 

 l(i) conclude that there are errors in all previous 

 determinations of the aberration constant. By 

 a new method they find Struve's value (20'445 ) 

 to be very nearly true, and they also find that 

 reflected and direct rays behave alike as to 

 aberration. 



Spectroscopy. Michelson and Morley have 

 found that interference bands obtained with the 

 hydrogen a line disappear with a difference of 

 path of 15,000 or 4~>,0()0 wave-lengths, and they 

 therefore conclude that it is a close double, the 

 components being separated by only ^ ff of the 

 distance of the sodium lines. Ebert denied the 

 validity of their conclusions, and Lord Rayleigh 

 criticised Kbcri's assertions. Kbcrt, now (" An- 

 nalen der Physik nnd Chemie," viii. 1891) 

 claims to have established that the observed 

 phenomena are not connected with duplicitv but 

 rather with the intensity of the light. G. John- 

 stone Stoncy (Dublin Uoyal Society. March 18) 

 has mathematically examined the cause of 

 double lines in the spectra of gases. On the 

 dynamical theory, apsidal motion (in its own 

 plane) of the ellipse of vibration of a molecule 

 would give rise to a pair of lines, and motion of 

 the nodes would have the same result. Such 

 motions may perhaps be ascribed, oy the electro- 

 magnet ic t heory, to the reaction of electric dis- 

 placi mentscaused by the oscillation of permanent 

 electric charges Hufner and Albrecht (Wiede- 

 inann's "Annalen," March) find that the ab- 

 sorption of light by water is greater the longer 

 the wave-length. But the curve of transmission 

 is not regular, showing sudden rises in the 

 regions of the D and G lines. Olszewski (Cracow 

 Academy of Sciences, January) has made im- 

 portant observations on the spectrum of liquid 

 oxygen. This had previously been considered 

 colorless, but by usinir a layer 30 millimetres 

 thick he found it to be a bright sky-blue. A 

 layer 7 millimetres thick showed absorption 

 bands in the orange-yellow; one of 12 milli- 

 metres showed three in the green and blue, and 

 the ISO-millimetres layer showed a fifth in the 

 red (Fraunhofer's A). He concludes that the 

 blue of the sky is due to the oxygen of the air, 

 confirming th opinion of Egoroff and Janssen. 

 Sir John Conroy (London Physical Society, 

 Feb. 13) has found that the absorption spectrum 

 of cobalt glass varies with temperature. Similar 

 changes in solutions may be ascribed to the 

 formation of hydrates or by partial di~-'ciation, 

 but neither of these explanations holds for a 

 solid. II. Kigollot (Paris Academy of Sciences, 

 .Ian. 5). in experiments on the absorption, spec- 

 trum of iodine, concludes that with an in 



f molecular weight of the solvent the absorption 

 band i* shifted to the violet end. and the mini- 

 mum amount <>( light received diinini-i 

 value. A. Coniu (I'm is Academy 



Dec. _',!) deduces flolll photographs of -; 



by I>r. '. Simony the following fa< t- <.,m-. ruing 

 the induct! I the atmosphere on the ultra- 

 violet solar .spectrum : 



Teneilffe .. 



Oontnugr . 



t,m 



170 



f tptctnu*. 





Polarization. Wiener (Wicdemann'a "An- 

 nalen," xl. ^(i:;, IMiO) allowed a vide beam of 

 polarized light to fall on a reflecting surface at 

 mi angle of 45, so that the redeetcd ray cuts 

 the incident at a right angle. If there is inter- 

 ference here, the direction of vibration of the 

 polarized light must be normal to the plane < f 

 polarization and perpendicular to the direction 

 of propagation. By using a thin photographic 

 pellicle he proves the existence of interference 

 fringes, and his results thus support the generally 

 n ceived theory of j:ola fixation. Dr. Fook (Berlin 

 " Berichte," February), assuming that the carbon 

 molecule is tetraht dral. shows that the dilTcn nt 

 effects of its apex and base on light will account 

 for the greater strength of one circularly 

 polarized ray in certain solutions, which is 

 generally considered to be the cause of their 

 power to rotate the plane of polarization of a 

 light beam. 



J'JiofpJiorefCfiice. E. Wiedemann (Beiblatttr 

 to Wiedemann's" Annah ii." i\. 1MU ; rcludes, 

 from experiments on Balmain's luminous paint, 

 that matter that emits more light than hent 

 is not necessarily the cheapest source of light. 

 In order to establish the contrary, account 

 must be taken of the entire transformation 

 of the energy of the light in the pn>< . 

 using it. His results are opposed to tli< 

 Langley ("Annual Cyclopedia," 1890. p. 714). 

 On the other hand. Prof. William 1'iookcs. in an 

 address before the Institution of Electrical 

 Engineers (Nov. 13), noted that the researches of 

 Hertz and Lodge have " unfolded tons a new 

 and astonishing universe." The wave-lengths < if 

 electric rays are constantly being reduced i 

 periment, and could we construct Leyden jars 

 of molecular dimensions, the rays might fall 

 within the narrow limits of visibility. Prof. 

 Crookes thinks that the phosphorescence of the 

 rare earths by electricity may be actually an 

 artificial product ion of these short electric rays, 

 and that if it could be produced more easily and 

 more regularly, as in the glow-worm and firefly, 

 it would be far more economical than any light 

 we know. Henri I5cco,uerel (Paris Academy. 

 March 1(5), using his father's well-known phos- 

 phoroscope to examine the spectra of various 

 phosphorescent minerals, find* that in chloro- 

 phane the spectrum varies with the \<-l> city of 

 rotation of the instrument. He concludes that 

 this is due to the presence of different sub- 

 that form definite compounds under certa 

 ditions of illumination and temperature. M. 

 Becquerel has also (ibid.. Nov. !i 

 formula; for the relation between the intensities 



