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February 20, 1891.] THE PHOTOGRAPHIC NEWS. 145 CAPTAIN ABNEY’S LECTURES ON COLOUR. Last Friday afternoon Captain Abney delivered the first of a set of lectures and demonstrations on “ Colour ” in the great room of the Society of Arts. The lecture was of a popular kind, the idea being to convey instruction in an attractive form, and on the basis of not assuming previous technical knowledge on the part of the auditory. Captain Abney, in introducing the subject, said that no natural phenomenon gives greater pleasure than that of colour. The scientific mind is not satisfied with merely receiving the pleasure which colour offers to the senses, but requires to investigate the reasons for the appearance of colours of varied kind. Art pays no attention to num bers, but it is the business of science to reduce colours to numbers, to make a statistical description. He thought that one of Turner’s pictures might be expressed by science by noting and giving description of the colour and intensity of each part of it. Colour depending upon light, it is therefore neces sary, in the first place, to go somewhat into the science of light itself. It is not possible, even if expedient, in that course to treat the subject of light exhaustively, nevertheless enough must be explained to make clear what had to be said with regard to colour. White light is composite ; its components are retarded to a different degree by passing through glass or other media; in other words, these components are differently refracted. No medium being perfectly transparent, even air retarded and absorbed a certain amount of light. Having explained that the light to be used in the ex periments (the electric arc) depended upon the disturbance of the molecules of the carbon points, the lecturer pro ceeded to give an idea of the minuteness of molecules, and followed this by referring to the rapidity of the vibra tions of the luminous rays. To illustrate this point it was mentioned that for certain rays there are as many vibrations in one second as there are seconds in twenty millions of years. The rate of vibrations of molecules was then discussed, and the absorption of certain rays analogically illustrated by the taking up of certain sounds by strings tuned to vibrate with the same rapidity as that belonging to the sounds thus absorbed. Colour was described as produced by the deprivation of white light of a portion of its constituents. It would, therefore, be an absurdity to speak of converting white into coloured light. That was an impossibility. When a coloured glass screen or bottle of coloured solution was placed in the path of a ray of white light, what happened was this. The atoms of the glass or of the solution were vibrating at the same rate as that of certain of the rays of light. The vibration of these rays was taken up by the atoms, and consequently did not pass through, whilst the vibrations of the remainder of the light were transmitted and produced the effect of colour. An apparatus for decomposing and recomposing the elements of light was shown, and its work projected upon the screen. Following this, the subject of fluorescence was taken up, and it was shown how certain rays were absorbed, and the fluorescent substance then gave out rays haying other rates of vibration ; thus rays from the invisible part of the spectrum might be made to stimulate an action corresponding to and producing visible rays. Interference was next described, and its effect in pro ducing iridescence in thin films illustrated by the pro jection of an image from a soap film, a gorgeous display of colour. Photographers who have the opportunity should find both interest and instruction from attending the present course of lectures, which, as has been mentioned, are upon a popular basis, although not on that account to be con founded with the trivial and often incorrect displays of popularised science which obtained a certain amount of favour many years since. OUR PHOTOGRAPHER, MR. BROWN, BY JAMES MEW. His name was Brown, and his ways were free, And he opened his place a week ago ; But he only took of our portraits three, Then married, and closed his studio. By each of his customers hangs a tale, And yet they were of the human kind ; There was not among them a single male— But I’ll tell you their stories, if you’re inclined. First came the parson’s wife ; with skill Were her faded charms repaired by art ; Her face—thought Brown—though it makes me ill, Might certainly make an artistic carte. Ah ! Brown has never been pardoned yet By this lady, rendered by art so fair, For he wrote on the back of her cabinet, “ Original (1) preserved with care.” Next came a widow advanced in years, A widow as mean as mean could be ; But Brown, he managed to quell her fears Of the cost, and showed her in poses three. “ How much would you take me for, Sir ? ” she cried, As she thought of the charge of his rival, Green ; And Brown, as his guileless smile waxed wide, Said, “ I’d take you, Miss, for about sixteen !” Last came to his door a maid of grace, And riches, and beauty, your heart to rive ; Said Brown, as he covered his blushing face, ‘ ‘ Can I be content with her negative ? ” “ How will you take me ? ” that maiden smart Asked. Said bewildered Brown, in verse, “ On the plate of my heart, a permanent carte, For richer or poorer, for better or worse.” The Physical Society.—At the annual meeting of the Physical Society, held last Friday at the Science and Art Department, South Kensington, Professor A. W. Reinold, F.R.S., presided. Professor J. Perry read the annual report, in the course of which it was stated that the Society now has 365 members. Mr. G. M. Whipple, Superintendent of Kew Observatory, proposed a vote of thanks to the Lords of the Committee of Council on Education for the use of the lecture theatre for the meetings of the Society ; also for the use of the scientific appliances on the premises for demonstrations. All this saved the Physical Society much expense, and gave it an advantage over the Royal Society in the giving of experi mental illustrations. Professor Sylvanus Thompson wished it to be generally known that the publications of the Physical Society are accessible to the public, and can be purchased. A paper by Sir John Conroy was read on “ The Influence of Heat on Coloured Media.” He heated a piece of cobalt glass, but not to its melting point, by means of a small burner ; of the three absorption bands which cobalt glass gives in the spectroscope, the outermost edge of the band in the red shifted a little in the direction of the ultra-red end of the spectrum when the glass became hot. Some farther particulars about facts made known at this meeting will be found in the “ Notes ” upon another page.