transactions' OF SECTION A. G39 



this phenomenon, and the behaviour of median lines when polar lines appear 

 near them. Fowler, who had previously ' examined these lines in the region 

 F to 0, pointed out their identity with enhanced lines and those weakened in 

 sun-spots, and considered that they might be regarded as high-temperature lines ; 

 but the writer's photographs, in which the intensities were the same on the two 

 poles, did not support this view. A subsequent paper by G. A. Hemsalech and 

 C. de Watteville'^ is of interest in this connection, because they find that 

 'enhanced' and polar lines constitute almost exclusively the spectrum of iron 

 given by the low-temperature Bunsen flame. This is evidence that chemical 

 action or electrical conditions are chiefly responsible for their appearance. Fabry 

 and Buisson have also independently examined the polar lines in an arc, but 

 they conclude that they are formed when the ions attain a certain velocity which 

 may be produced either by a potential fall or an elevated temperature. Hart- 

 mann has discussed the conditions concerned with the production of the 

 'spark' line of magnesium X = 4481 in an arc spectrum, and from its strong 

 appearance in a weak arc he decided that temperature was not the criterion for 

 its existence. 



3. The Zeenian Effect in Sun-spots, By Professor J. Larmor, Sec. R.S. 



4. On the possible Existence of Steam in the Regions of Sun-spots. 

 By Rev. A. L. Cortie, S.J., F.R.A.S. 



At the Leicester meeting of the Association the probability of the lower 

 temperature of the sun-spot regions relatively to the photosphere was derived 

 from a comparison of the behaviour of the bands of titanium oxide in the spectrum 

 of Mira Ceti, at a more or less brilliant maximum, and the bands of the same 

 compound in the spectrum of sun-spots.^ The question at present discussed is 

 whether the reduction of temperature over a sun-spot is sufficiently great to 

 permit the formation of water-vapour in the form of superheated steam. For 

 more than twenty years in the observations of sun-spot spectra made at Stony- 

 hurst in the red and yellow regions numerous lines have been recorded with the 

 dispersion used as widened or atl'ected in sun-spots, which are coincident with 

 lines due to water-vapour. One obvious explanation is that true solar lines^are 

 so close to the water-vapour lines as not to be separable, even with very great 

 di.'spersions, and that the widening is due to the solar lines. Using a much more 

 powerful combination of telescope and .spectroscope than the tele-spectroscope at 

 Stonyhurst, Dr. Mitchell, of the Princeton Observatory, was unable to detect 

 these lines as widened in the spectrum of sun-spots.^ The region X 5900-5950, 

 which is very rich in such lines, has been carefully studied and measured on a 

 photograph in the third order of a large flat-grating in the spectrum of a big 

 sun-spot secured on July 81, 1906. The details of the measurements are set 

 forth in a table. Of 91 lines measured, 64, or 70 3 per cent., are due to 

 water-vapour, and of these 64, 29, or 45'3 per cent., are affected, either widened 

 or darkened, in the sun-spot. In the photograph measured the sun-spot spectrum 

 is not isolated from the photospheric spectrum. But in the photographic map 

 of Professor Hale and Mr. Ellerman, iu which the sun-spot spectrum is isolated, 

 16 of these 29 lines are present, the dispersion being much greater than that 

 employed at Stonyhurst. Professor Fowler has shown ' that a great number 

 of the bands in sun-spot spectra are due to magnesium hydride, and Mr. Brooks,*^ 

 from a laboratory study of this same spectrum, concludes that it cannot be pro- 

 duced without the presence of water-vapour. Hence it may be concluded that 

 the lowering of temperature in the regions of sun-spots, iu which the chemical 



' Monthly Notices, 67, 154, 1907. ^ C.R., June 1908. 



' ABtrophi/.ncalJournal, xxvi. 2, September 1907. ' Jbid., xxii. I. p. 29. 



» M.iY. R.A.ii., Ixvii. No. 8. « Fruc. U.S.A. , 80, No. 537. 



