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72 THE PHOTOGRAPHIC NEWS. [January 23, 1891. apt to engender a turn for that analysis which is opposed to feeling. There is a good deal of fine poetry which the world enjoys that would not stand the test of the gram marian’s scrutiny, and much artistic romance that would not bear the touch of the Ithuriel’s spear of a scientific Mark Twain. I must not carry this argument too far, or it would be made into an excuse for not learning anything -—there is always danger in extremes—and I may lay my self open to be misunderstood. I have a great reverence for science, but think that the artist should take just as much as would be good for him, and no more.* I know that this is not the opinion of those who usually decide upon what a photographer must learn, and that a student can get a certificate that he knows all about pho tography when he knows the complete chemistry of the operation short of the composition of the image ; and, indeed, in strict technical truth, so he does, but he has only learned the technical application of his materials, and has yet to know how to put them to artistic use in the making of pictures, and the mischief is that when students go for the advanced science of photography they some times get lost in it, and the result is that it often happens that learned chemical papers are read against each other by great scientists at photographic societies to prove or disprove a simple fact that a mere tyro could easily settle by a couple of experiments. It is pleasant to see that there is at last to be some addition made to the usual chemical course at at least one great teaching centre, and that the managers of the Polytechnic Institution are about to add lectures on art as applied to photography to their programme. It is to be hoped that if a great photographic institute should ever be founded, that it should not be a mere chemical laboratory, but that students should be taught to put the art to use. Abstract science must be held in all respect, but the average photographer is a practical man, and wants to know how to make pictures. The Photographic Club.—On Jan. 28th the annual lan tern and musical entertainment will take place ; subject for Feb. 4th, “ The Tone of Lantern Slides.” The Croydon Microscopical Society (Photographic Sec tion).—January 16th was a lantern night, when a good selec tion of over 200 slides, by members, were passed through the lantern during the evening. IThe next ordinary meeting will take place on the 6th, and lantern night on February 20th. Last Saturday the employees and friends of Messrs. Percy Lund and Co. met in the Teetotal Hall, Bower Street, Bradford, Yorkshire, for their annual winter social evening. Proceedings commenced with a tea, to which over seventy persons sat down, and after the tables had been cleared, an excellent variety programme was gone through. As a number of the employees are young people in their “teens,” a departure from the usual rule at such gatherings was made by introducing a few old- fashioned games, such as blind man’s buff. The platform items of the programme included a couple of dramatic sketches, a short comedietta, and a variety of vocal and instrumental music, and recitations. * This paragr aph was written same weeks ago, and I c nnot help referring to a sincular illustration of its truth which has just occurred, and wil probably be announced to-day. A study of Messrs. Hurter and Driffield’s scientific paper-, aided by a few minor considerations, has so convinced Dr. Emerson that true values cannot be obtained by photography that, with a courage worthy of all prais:, and which I, his old opponent, respect, he has renounced “ Naturalistic Photography,” proclaimed its death, and written its epitaph. The throwing up of a cherished bel'ef which has occupied the thoughts of many of the best years of a studious life, through scientific conviction, is a heroic proceeding, which, while it commands our admiration, makes one almost thankful for ignorance, and for freedom from the nightmares of science. PHOTO-ELECTRICITY AT THE PHYSICAL SOCIETY. At the Physical Society on December 12th, 1890, with Professor W. E. Ayrton, president, in the chair—- Mr. Shelford Bidwell, F.R.S., showed some experiments with selenium cells. The crystalline variety of selenium was, he said, most interesting to physicists, owing to its electrical resistance being greatly diminished by light. This property was shown experimentally with different forms of cells, the con struction of which was explained. The form recommended was that in which two copperwires are wound neareach otherround a slip of mica, and the spaces between the wires filled with selenium. The wires form the terminals of the so-called “cell,” which, before being used, is annealed for several hours at a tempera ture above 200° C. Many such cells were made in 1880, 1881, and their sensitiveness to light remained unimpaired during 1882. In 1885, however, several were found less sensitive, and others totally useless ; only one out of thirteen retained its sensibility till September, 1890. The loss of sensitiveness Mr. Bidwell believes due to an excessive amount of selenide of copper being formed, for, although some selenide is essential to the satisfactory working of the cell, too much is fatal to its action. The selenide of one defective cell was electrolyzed, red tufts of amorphous selenium appearing on the anodes. A white substance, resembling moist calcium chloride, was also present; this he believed to be oxide or hydroxide of selenium. Small polarisation currents had been obtained from selenium cells. A lecture apparatus illustrating the properties of selenium cells was exhibited. It consisted of a cell connected in series with a relay and a battery. The relay was arranged so that it might either ring a bell, or light an incandescent lamp. When the bell was joined up, it remained silent as long as the selenium cell was illuminated, but on screening the cell the bell rang. By using various coloured glasses as screens, the effect was shown to be due to the red and yellow rays. A similar experiment with the glow lamp was very striking, for on turning down the gas-lamp illuminating the cell, the electric lamp lighted, and was extinguished on turning up the gas. This demonstrated the possibility of an automatic lamp-lighter, which would light or put out lamps according as they are required or superfluous. Amongst the other practical applica tions suggested were, announcing the accidental extinction of railway-signal lamps or ships’ lights, and the protection of safes and strong rooms. Prof. Minchin said that he had lately constructed cells of a different kind from those shown by Mr. Bidwell, and found that they gave an E.M.F. when exposed to light. For his purposes the long annealings were quite unnecessary, and acompletecell could be made in ten minutes. One of hiscells gave an E.M.F. of over 0-25 volt as measured by an electrometer, by the light of a fog. Their promptness of action falls off in a day or two, but if they are kept on open circuit, a week has no effect on the final E.M.F. On closed circuit, however, they deteriorate. Prof. S. U. Pickering said that both oxides of selenium were deliquescent, and the author’s conclusion as to the white substance formed by electrolysis was probably correct. Prof. S. P. Thompson believed Prof. Graham Bell had tried platinum instead of copper, and found that the selenium cracked off in annealing. He had also found that it was only necessary to carry on the annealing until the characteristic slate colour appeared. Mr. Bidwell’s experiments, he said, showed the possibility of seeing at a distance, and had also suggested to him that the effect of screening might be utilised for driving a completely detached pendulum electrically. Prof. Forbes said that silver sulphide, when electrolyzed, presented appearances resembling those noticed by Mr. Bidwell in copper selenide. In reply to questions from the President and Prof. Perry, as to whether the low resistance and unsensitiveness of old cells was due to moisture, Mr. Bidwell said that drying them had no effect; baking restored the resistance but not their sensi tiveness. Speaking of the effect of annealing cells, he said this