NATURE [Nov. 6, 1884 



inclosed in a lead pipe, and to the columns by two cables 

 of seven strands of No. 12. A separate return cable runs 

 from each lamp to the hut, where it is connected to the 

 necessary resistances, made of strip iron, and from there 

 back to the dynamo through two cables of nineteen No. 

 12's. There is altogether very nearly a ton of copper in 

 the various leads and branches. Besides these leads the 

 centre chamber is connected to the circuit of the Sun 

 light machine, so that, should any accident occur to the 

 main circuit or midline, Sun lights could be substituted 

 for the hand lamps. 



As the falling spray cuts off the light from below when 

 the jets are at their highest, a light is placed in the top of 

 the clock tower to illuminate the top of the jets. This 

 light is a focus-keeping Siemens automatic lamp, and 

 takes a current of fifty amperes, supplied by a small 

 Crompton-Burgin machine. The lamp is inclosed in a 

 cast-iron casing swung on trunnions, and in front of it is 

 a fifth-order holophotal lens by Messrs. Siemens. 



The various coloured glasses are fixed in frames or 

 sashes arranged with counterweights, in the same way as 

 an ordinary window. Some of the best effects of colour 

 are also obtained by sheets of gelatine, of which a large 

 number are fastened end to end, and fixed to two rollers, 

 so that they can be wound from the one to the other, and 

 thus passed through the beam of light. 



As the men in the centre chamber cannot see the 

 effects they produce, it is necessary to direct them from 

 the outside, and this is effected by an elaborate system of 

 electric bells and disks, which are worked from the clock 

 chamber below the last-described holophote. In this 

 chamber sits Sir Francis Bolton, with a treble row of 

 " pushes " in front of him, all labelled, by touching any of 

 which a corresponding disk or bell is worked in the 

 island. There are four bells — a call bell, an " on " bell, 

 an "off" bell, and a lamp bell — and two indicator boards 

 with eight disks each, and one with four. One board is 

 for the water valves, which are each painted a different 

 colour, with the corresponding colour on the disk, and 

 the second board for the coloured glasses over the holo- 

 photes. The disks on the small board refer to the corner 

 lamps, and by their means Sir Francis can direct any colour 

 to be placed over any one of the lamps by touching the 

 push corresponding to the lamp and the push marked 

 with the colour which he wishes to show. The working 

 of the holophote at the top of the clock is directed in the 

 same way. 



EXPERIMENTS WITH COAL-DUST AT 

 NEUNKIRCHEN IN GERMANY 



TOURING the course of the last summer the Royal 

 •*—' Prussian Fire-damp Commission has carried out a 

 series of experiments in the Saarbriicken mining district 

 with the view of ascertaining the influence which coal- 

 dust has, alone and in conjunction with fire-damp, in 

 propagating explosions in mines. The apparatus and the 

 mode of experiment were suggested by retired Bergwerks- 

 director and Bergassessor Hilt, of Aix-la-Chapelle, who 

 is a member of the Commission, and the results hitherto 

 obtained have been of the most interesting kind. 



The experiments are conducted at the Royal Coal- 

 Mine, Konig, near Neunkirchen, where there is a blower 

 of fire-damp at a depth of 131 yards below the surface. 

 The quantity of fire-damp given off by this blower amounts 

 to about o'9 cubic foot per minute, consisting of S6 per 

 cent, of light carburetted hydrogen mixed with air, &c. It 

 has been in existence for the last two years. The fire- 

 damp is brought a distance of 1200 yards in pipes, and 

 collected in a small gasometer whose capacity is 176 cubic 

 feet. 



Dr. Ad. Gurlt of Bonn lately called my attention to the 

 fact that over two hundred experiments made with this 



apparatus on a large scale had proved the correctness of 

 my theory of great colliery explosions {Proc. Roy. Soc, 

 vol. xxiv. p. 354, Sec.)) anc ' at the same time suggested 

 that a visit to Neunkirchen would be of interest. 



Accordingly I proceeded to the scene of the experi- 

 ments on October 25, accompanied by Mr. We Thomas 

 Lewis, one of the members of the Royal Commission 

 on Accidents in Mines, and we were met there by Dr. 

 Gurlt, who had travelled from Bonn for the purpose, and 

 by Herren Prietze, Nasse, Margraf, and Kreuser, directors 

 and assistant-directors of Konig Grube and other Royal 

 mines of the neighbourhood. Herr Margraf, under whose 

 superintendence all the experiments are and have been 

 made, has most kindly furnished me with a detailed 

 description of the apparatus and of the experiments wit- 

 nessed by Mr. Lewis and myself, and I am glad to avail 

 myself of, and shall endeavour to reproduce, his account 

 as nearly as may be, allowance being made for the diffi- 

 culties of exact translation. 



The experiments are made in a horizontal wooden 

 gallery 167 feet long, closed at one end, and having a 

 horizontal branch gallery 33 feet long standing out at 

 right angles to it at a distance of 93 feet from its closed 

 end. Both the main gallery and the branch consist of 

 elliptical rings of double T-iron lined internally with 

 planks 16 inch thick, which abut closely together and are 

 grooved and feather-jointed lengthwise. The greater 

 axis of the ellipse stands vertically, and is about 5 feet 

 7 inches long ; the lesser axis is 3 feet 1 1 inches 

 long. The main and branch galleries are both em- 

 bedded in the pit-heap to such a depth that the rubbish 

 is level with their top on one side and reaches to three- 

 quarters of their height on the other side. Along the 

 exposed part of the latter side there is a row of windows, 

 thirty-two, in the main gallery, and three in the branch 

 gallery, situated somewhat more than a yard apart. 

 They are formed of sheets of glass about jj inch thick set 

 in cast-iron frames. There are also a number of openings 

 in the top of the main gallery, one of which, near the 

 closed end, is an ordinary man-hole, which can be closed 

 by a man-hole door like that of a boiler, and serves 

 as a means of ingress and egress. The others are 

 circular, about 9 inches in diameter, and are lightly closed 

 with wooden plugs attached to chains, which act as safety 

 valves. All these openings assist in the removal of after- 

 damp after an explosion. 



The closed end of the main gallery is sunk about 

 3 feet 9 inches into a block of masonry whose dimen- 

 sions are 12 feet 4 inches long, 9 feet 9 inches wide, 

 and 13 feet high. Seven cast-iron cannon, with a bore 

 similar to that of a shot-hole in hard ground, are built 

 into the block in the position shown in the figure 

 opposite, so that their mouths are flush with the face. 



There are two holes near the top, two near the bottom, 

 and three in the middle, grouped symmetrically in relation 

 to the two axes of the ellipse. The middle hole is 37 

 inches deep by 1-57 inch in diameter ; the others are 31^ 

 inches deep by 1 '37 inch in diameter. The axes of the 

 two upper and of the two lower holes are placed in such a 

 position that they form the angles of a four-sided regular 

 prism whose apex is situated in the axis of the main 

 gallery at a distance of i6'4 feet from the face. The axes 

 of the three middle holes constitute a bundle of rays which 

 meet at the same point as the last. Wooden hoops pro- 

 jecting inwards from the sides are placed at various dis- 

 tances apart in the main gallery within the first 65J feet 

 from the face. By fastening cloth diaphragms to these 

 hoops, compartments of various capacity can be formed, 

 that of the first next the face being 705 cubic feet. 



The shots are fired electrically with Abegg's fuses by 

 means of an exploder made by .Mahler and Eschenbacher 

 of Vienna. The charge, which consists of 230 grammes, 

 or about half a pound, of powder, occupies a length of 

 S64 inches in the central hole, leaving room for rather 



