POLYTECHNIC INSTITUTION.
CURIOUS to see Mr. Bern's Magnetic Printing Telegraph, we made one of the-throng that crowded the spacious galleries of this repository of
the wonders of science and art, filling its lecture-theatres to over-flow- ing; and, besides the special object of our visit, we were gratified by the sight of several other novel and beautiful inventions that have been lately added to the collection of curious contrivances.
The peculiarity of this Magnetic Telegraph is, that it prints the in- formation it conveys, without the intervention of any other than the person communicating the intelligence : thus, by its means, news brought to Portsmouth could be transmitted in cipher to the Admiralty and printed there instantaneously, without any previous signalling, or the presence of any person at the place of printing; and a speech in Parliament or message from the Throne might be reported at Edin- burgh while the words were just uttered in London. Had the possi- bility of such a thing been hinted at only a very few years ago, it would have been ridiculed as the raving of a crack-brained projector ; yet the practicability of accomplishing this is demonstrated by Mr. BAIN'S apparatus, which is scarcely less admirable for its simplicity than its marvellous action.
A dial• plate marked with the letters of the alphabet is traversed by an index-hand, which is kept moving round it by the agency of electro- magnetism : this motion is communicated, through a wire of any re- quired length, to an horizontal wheel, on the edge of which are cut in relief the letters answering to those on the dial : the wheel revolves as the index does, its lettered edge coming in contact with a cylinder charged with ink : when the hand of the dial is stopped at a particular letter, the corresponding letter is impressed by the action of the ma- chinery upon a cylinder covered with white paper: this action is re- peated till the whole of the communication is made. The unerring precision and neatness with which this action is performed is beautiful. The same principle is applied to communicate the action of clock-work, so that one steady-going clock will suffice to point the time on any given number of dials at any distance.
The advantages of the Magnetic Telegraph over the ordinary wooden post and arms are obvious,: not only is the rapidity, facility, and cer- tainty much greater, but intelligence could be conveyed at night and in foggy weather, when the other is useless. The addition of the printing- power is a very important improvement upon the Magnetic Telegraph in use on the Western Railway, since it prevents the possibility of mistake by recording the message itself. Mr. BAIN, the inventor, is generally in attendance to exhibit the apparatus in action and answer any inquiries ; though Mr. BACHOFFNER'S explanatory lecture is so clear that few can misunderstand his description. The Microscopic Exhibition is preceded by a very pleasing series o, Dissolving Views of natural size, and most powerful effect of coloar : the rapid succession in which the several scenes appear, their outlines melting each into the other so insensibly that the fading view is only obliterated by the vividness of the coming scene, has a magical effect. Among the best of these fleeting pictures are those in which PROIIT'S vigorous style is recognized : the tone of colour in these paintings is intense ; and if the whole of the disc were as bright and clear as the focal point, their effects would be beautiful indeed. The quality of the art in the original, we would remind the exhibitors, makes a ma- terial difference in the brilliancy of the dissolvent image.
The Photographic Miniatures are in as great request as ever ; and practice has enabled the persons engaged so to place the sitters as to pro- duce an agreeable arrangement of light and shade on the countenance: a gold tint is thrown over the surface occasionally, which obviates the livid appearance objected to by many. Some of the sun-limned minia- tures are lively and agreeable, others the reverse ; but in all the likeness and execution are extraordinary. As documents to assist the painter, they are extremely useful : we know an artist who never paints a por- trait without having a photograph of the sitter to refer to.
The production of medals and copper-plates by the Electrotype process is another of the recent discoveries exhibited here, whereby the elements of nature are made to produce works of art.
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