778 BBPORT — 1881. 



To prepare the iustruments for work, a piece of sensitised paper is wrapped' 

 round the cylinder of the receiver, and the platinum point pressed gently upon it r 

 the pinhole in the transmitter is brought to the brightest part of the focussed 

 picture, and the variable resistance in the circuit of the local battery is so adjusted 

 that the two currents, passing through the paper in opposite directions, exactly 

 balance each other. The cylinder and the box are then moved to their extreme 

 positions, and all is ready to commence operations. 



The two spindles are caused to revolve uniformly and synchronously. The pin- 

 hole, in the course of its up-and-down path, will cover successively every point of 

 the projected picture, and the amoimt of light falling at any moment upon the 

 selenium cell will be proportional to the illumination of that particular spot of the 

 picture which, for the time being, is occupied by the pinhole. When the pinhole 

 is in the dark, the resistance of the selenium cell is increased, the current from the 

 local battery predominates, and the platinum point traces a dark brown line upon 

 the paper ; but when the pinhole happens to be passing over a bright part of the 

 picture, the resistance of the selenium is diminished ; a stronger current is then 

 opposed to that from the local battery, and the line traced by the point is enfeebled 

 or altogether broken. The close spiral line thus described, with the breaks in its 

 uniformity, constitutes a picture which, if the instrument were perfect, would be a 

 monochromatic counterpart of that projected upon the transmitter. 



The pictures hitherto actually transmitted by this experimental apparatus are 

 simple designs in black and white, painted upon glass, and projected by a magic 

 lantern. The image of a butterfly with well-defined marks upon its wings, and a 

 rude drawong, in broad lines, of a human face, are among the objects which have 

 been most successfully reproduced. But with a more delicate, selenium cell and 

 more sensitive paper, there is little doubt that the efficiency of the instrument 

 might be almost indefinitely increased. 



2. On the Swan Incandescont Lamp. By J. W. Swan. 



3. On Electric Lighting as applied to Goal Mines. By Andrew Jamieson, 



In the discussion which followed the exhibition of Swan's lamp at the Society 

 of Telegraph Engineers in October last, Professor Tyndall remarked that probably 

 this form of incandescent lamp could be adapted for use in coal mines as a safety 

 lamp. Since then, two practical trials have been made with that object in view, 

 the one at Pleasely Colliery, near Nottingham, the other at Earuock Colliery, 

 near Glasgow. The circumstances under which the lighting has to be produced 

 and maintained are new and ditfiereut in many respects from that now being carried 

 out above ground in our halls, houses, and open spaces. Dangers and dithculties 

 peculiar to the situation have to be guarded against or overcome, such as explosive 

 gases, subsiding walls or seam-roofs, continuous darkness, &c. Long lengths of 

 leading wu-e have to be dealt with, involving many branches or oS'shoots, 

 requiring considerable mechanical skill and still more electrical knowledge, before 

 a suitable distribution of the eleetric current is effected, and the desired uniformity 

 and intensity of light obtained. Particular interest is at present being manifested 

 by mine owners, managers, and engineers to know the commercial value of the 

 light, or, in other words, whether the possible increased light and safety of Swan's 

 lamps over the methods hitherto adopted will residt in an economy and in an 

 increased output of coal for the same expense of labour. The author described 

 the apparatus used at Pleasely and Earnock collieries, with models of strong miners' 

 lanterns encasing Swan's lamps, and of airtight contact-makers of various 

 designs and patterns, for preventing the inevitable spark (which always takes place 

 upon disconnecting leading wires or lamps) from causing danger in a fiery mine. 

 He pointed out that the plan of joining up a number of Swan's lamps in single 

 parallel, with a self-exciting Gramme, Siemens, or other form of dynamo-macliiue. 



