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ant’s solicitor that ‘ he had a boy in court who knew defendant very well, and when the portrait was sent home ho could not recognize it.” This was a powerful but not quite convincing argument, because, although the boy might not recognize the portrait, it did not necessarily follow that it was the fault of the portrait—it might have been the fault of the boy. On another column, Professor Donkin is good enough to tell us something about his photograph of the “ Dent du Geant,” which forms our illustration for this week. Two views of the Exhibition. 1. On Monday last, before the lantern show commenced : Amateur, looking at Mr. Robinson’s pictures: “ A professional, of course; you see they’re at it all day long—never do anything else—one can’t hope to rival them." 2. After the gas is turned down. Professional, looking at Mr. Gale’s slides on the screen : “ Oh! amateur, I daresay: nothing else to do—of course he can make slides.” Moral (from Burns) : “ Ob, wad some, &c., &c." Photography in colours. Many a photographic student would like to know what has really been done, and what has not been done, to solve the problem. Dr. Liesegang has had the happy idea to issue a little volume on the subject, « Die Heliochromie," which places before the reader all that Becquerel, Niepce, and Poitevin discovered in this interesting field of research. The labours of these three investigators, who worked with most success to reproduce colours in the camera, are succinctly reported in Dr. Liesegang's book, as well as the early essays of Sir John Herschel and Robert Hunt, the former of whom, it may be remembered, succeeded in producing the tints of the spectrum upon a Daguerreotype in 1839, colours that disappeared again very rapidly, even in the dark. The annual value of the sun’s heat, according to Profes sors Roscoe and Balfour Stewart, is greater at Kew than at London in the proportion of 100 to 58. It does not, of course, follow that there is the same tremendous falling off of actinic power in London sunshine, but this is more than probable. Certainly London photographers seem to bear out the view, for there are not many first-class firms that do their printing in the metropolis. Most of them have printing and copying establishments in the suburbs, where, in all likelihood, there is nearly fifty per cent, more light. It was only the other day that the Kew statistics told us on the sea coast there was much more sunshine than inland. An interesting table of velocities has been drawn up by Mr. James Jackson, the librarian of the Paris Geographi cal Society. He begins with the velocity of a man walk ing two miles and a half an hour, and, after alluding to the respective velocities of an ordinary wind, of a race horse, of an express train, of a carrier-pigeon, of a hurri cane, of sound in air and water, he brings us at last to the velocity of heavenly bodies, of electricity, and finally, of light. But Mr. Jackson has left out one important velocity, which has only been recently computed, and which is of singular interest, since it represents the only earthly agent known to man with a velocity quicker than sound in water, although naturally less quick than elec tricity and light: we mean the detonation of the photo grapher’s old friend, guncotton. Abel and Noble have computed that a train of guncotton, fired with a fulminate fuse, will transmit the detonating action at a speed of from 17,000 to 19,000 feet per second. In other words, deto nation travels at the rate of 200 miles a minute, while next in order comes electricity travelling through a submarine wire at a speed of some 12,000,000 feet per second. Mr. Crosby’s photographs of the St. Leger should augur a good time coming for photographers. The horses aie going, we are told, “ at their highest speed, and absolutely sharp, the features of the jockeys being recognizable in two or three instances.” If good racing pictures can be pro duced with the jockeys recognizable, these will have a ready sale, and must command a high price. A country photographer writes“ Yesterday I visited the Exhibition, and was pleased with it, except the appa ratus, as I had looked forward to seeing a more represen tative show of the various appliances, with some one to explain the working of the various shutters, &c. Many were the questions asked, but no one appeared able to answer them.” A few weeks ago we referred to a proposition which had been laid before the Corporation of London, that a picture gallery should be added to the Guildhall Library. It now appears, from a statement made by the Chairman of the Libraries Committee last week, that the Committee had taken no steps to provide, or even to suggest, a pic ture gallery. The chairman was good enough to say that the time was very opportune, but hinted that the merchants and traders of the City of London should bear the expense, rather than the Corporation. His argument was an odd one. He remarked that “the scientists were the true warriors of the present day ; they conquered the forces of nature, and laid them at the feet of the merchants. If the merchants were to do themselves justice, they would seek to raise a picture gallery, and place at the disposal of the Corporation funds for a building and for memorials to the men of this century by whom they had profited so largely.” In other words, because science had assisted the merchant, he should return the compliment by honour ing art. But if the merchant really wished to honour science in an artistic way, he could very easily do it, as we have before suggested, by providing a gallery for a com plete collection of views of London, not only of old build ings—the interiors of the City Halls, for instance—but also of the streets as they are now seen. No city in the world is so full of associations, and no city is undergoing change so rapidly. An exhaustive series would be of intense interest.