TRANSACTIONS OF SECTION A. 573 



MONDAY, AUGUST 24. 

 The following Reports and Papers were read : — 



1. Report of the Committee on Researches on the Ultra-Violet Bays of the 

 Solar Spectrum. — See Reports, p. 147. 



2. Comparison of Eye and Hand Registration of Lines in the Violet and 

 Ultra-Violet of the Solar Spectrum, against Photographic Records of 

 the same, with the same Instrtimevt, after a lapse of several years. 

 By C. PiAZZi Smyth, LL.B., F.R.S.E. 



A comparison of tlie plates seems to lead to such practically useful conclusions 

 as the following : — 



1. Ttoo photographic representations are far more trustworthy than three or 

 probably a much greater number of hand-drawn views of solar-spectrum lines, 

 even when the eye imagines it sees them very clearly. 



2. The photographic principle records with ease, and the utmost vigour of 

 black, white and grey of various shades, a world of objects in certain spectral 

 regions where the eye can see nothing whatever. 



3. What photography depicts in such cases is what the human eye ought to 

 see, and would see were it divinely perfect simply as an eye. 



4. The ordinary spots, pin-holes and dust-marks, which too often abound in 

 photography, never assume such shapes as might lead to their being mistaken by 

 any experienced observer for a single one of Nature's solar-spectrum lines of light 

 or shade. 



5. The frequent errors, and then ail-pervading effects, fallen into by some 

 photographers in the way of over or under exposure, and over or under develop- 

 ment, may prevent the absolute intensity of any one line, on one plate alone, being 

 usefully quoted as a scientific datum. Bat the relative intensities, and innumerable 

 distinctions in hue and shape, of thick or thin, dark or light, closely arrayed or 

 widely scattered, flutings gradating towards the violet or towards the red end, 

 and regularly or irregularly spaced lines on the same plate, are full of most 

 important and instructive particulars. While they mostly hold good also, from 

 plate to plate of the same parts of spectral space, on all the proofs that niay be 

 taken both day after day, and through a very wide range of all the possibilities of 

 perversion and misuse which may be humanly committed upon this most exquisite 

 aid, viz. photography, to the noblest of the senses of man, vision. 



6. In principle, all this has long been known to advanced workers in every 

 civilised nation. But as it is not everywhere yet utilised to the extent it might 

 well be, it is hoped that this further and rather multitudinous example, on an 

 extreme scale too, of spectral separation, and capable of showing such a Titanic 

 instance of a dark thunder-cloud-looking column as ' Great K,' by pure photo- 

 graphy only eight months ago, in a solar-spectrum telescopic field which was at the 

 time absolute emptiness to the eye, may be useful in calling increased attention to 

 similar and more extensive employments of photography in the future. 



3. Note on Observing the Rotation of the Sun with the Spectroscope. 

 By G. Johnstone Stoney, M.A., D.Sc, F.H.8. 



In this note the author described an arrangement for conspicuously exhibiting 

 to the eye the rotation of the sun by the spectroscope. The sun's light, after 

 reflection from the mirror of a heliostat, is received by a telescope lens which 

 forms an image of the sun on the slit of the spectroscope. The lens is attached to 

 a vertical board, and two screws are partly screwed side by side into the board 

 and at some distance above the lens. The projecting heads of the screws rest on a 



