The Optical Magic Lantern Journal (June 1899)

74 The Optical Magic Lantern Journal and Photographic Enlarger. fast enough, he turns the crank shaft 9 to the left, thereby lifting the friction wheel 6 away from the centre of the friction disc 5, and increasing the speed of rotation of the worm shaft 7. When the portion of the web is reached that has shrunk a little, so that a slower speed is necessary, and opposite motion if the crank shaft 9 prcduces the desired result. After passing through the machine the web is wound up on the winding drum or wheel 35. It is evident that as the web is wound up on this drum, and the diameter of the outer circle increases, the speed of rotation of the drum must decrease, so that the circumferential speed shall remain approximately uniform. This is accomplished automatically by reason of tke fact that the driving worm shaft 52 is ordinarily held by its own weight. When the worm shatt is rotated by the friction disc, the resistance to motion of the worm wheel 55 causes the worm 54 to start to screw up on the worm wheel; thus raising the worm shaft and carrying the | friction wheel higher up on the friction disc, and its action con c= of the worm shaft has a“ become such as to put ju” the proper and pre which is winding up 7 upon the reel 35 mounted upon the L a shaft 56 of the worm , wheel 55, and it will g eed appear that as the Tc 6 diameter of this 4 jaa 7 Srows” greater, the 4 [0 friction wheel 51 will [Lye be carried further up 4s a] | upon the friction disc ip | 5, thus reducing the 3 + t 2 angular velccity of the i web reel, and main taining the tension upon the web practically uniform. It is frequently desirable, after a strip of film has been wound upon one of _ the wheels 34 or 35, to remove the strip therefrom bodily without unwinding it, and te place another strip thereon. In order that this may be done one portion of the rim of the reel’ is hinged, as shown in connection with the reel 35 in i 53 AW ssi] Fig. XNTIII tinues until the speed | determined amount of | tension upon the web |: Fig. XXI. Being hinged this section is capable of being swung inward, as shown in dotted lines in Fig. XXI., thus loosening the film somewhat. The band 63 prevents the elasticity of the film from taking up the slack which is produced when the hinged section of the rim of the reel is swung inward. The band 63 is provided with projections 64, which are adapted to enter slots between the body of the rim and the hinged section 65, 80 holding the band in place on the reel. The ends of the strip of metal which forms the band 63 overlap, and are not riveted together at the very end, so that a slot is left into which the end of the film when folded over may be placed, in order to hold it to the band. A latch 66 is provided to hold the hinged section 65 of the rim of the reel in place when the reel is in use. 16388 of 1897. A New Light. By G. R. BAKER. WA 2 lighting has been so great that many scientific men have been experimenting with a view to discover some of the rare earths AS that could be used in a form that would I? be durable, if not everlasting, and there# fore not of the delicate nature of the well-known mantles of Welsbach. Professor Walther Nernst, of the University of Gottengen, has invented a most ingenious and at the same time simple electric incandescent lamp that bids fair to revolutionise electric lighting. It is claimed for it that it is extremely durable, if not quite indestructible, and not of such a limited life as the filament of the ordinary (Edison or Swan) incandescent electric lamp. Nernst, by choosing a material that will stand a lighter temperature than carbon, gets a_ strong substance to work with, but as these materials, in the ordinary course of things, are bad conductors of electricity—in fact when cold are insulators—they have rarely been employed, even in experimental work. In the Nernst lamp the material is worked up into little white rods, each of which is mounted on two platinum wires, and a little paste, made of refractory oxides, applied to the joints. This has to be heated in order for the material to conduct electricity, but a very little rise in temperature is necessary, and can be performed by either a small spirit lamp or by a match. It can also be automatically heated by electricity, and