I873-] 



Physics. 



549 



of hydrogen spectrum tubes, and the whole enclosed from behind with a board 

 covered with white paper. The reflection from the white paper fills the whole 

 opening representing the prominence with crimson light, so that the tubes are 

 not noticed. Fig. 6 shows the general appearance, and Fig. 7 the arrangement 



Fig. 6. 



Fig. 7. 



of the tubes. President Morton also stated that he was preparing some spectrum 

 tubes with meteoric hydrogen, so as to have what might be considered as a 

 real solar-prominence specimen. 



Electricity. — The improvements in magneto-electric machines follow each 

 other in rapid succession. Hardly is M. Gramme's machine announced ere 

 Mr. Wild, who has long been known in electrical circles as one devoting great 

 attention to, and bringing forward important inventions in, magneto-electricity, 

 introduces a machine with multiple armatures, producing a greater number of 

 currents for one revolution of the axis than has hitherto been obtained. 

 Although this machine has for many practical purposes been superseded by 

 the continuous current generator of M. Gramme, its importance in the pro- 

 duction of the electric light must not be overlooked. It consists of a circular 

 framing of cast-iron firmly fixed by stay-rods. A heavy disc of cast-iron is 

 mounted on a driving-shaft running in bearings fitted to each side of the 

 framing; one of these bearings is carefully insulated from the framing by 

 ebonite, and also from the shaft by a cylinder of the same substance. Through 

 the side of the disc, and parallel with its axis, sixteen holes are bored for the 

 reception of the same number of cores or armatures. Around each inside face 

 of the circular framing, and concentric with the driving-shaft, sixteen cylin- 

 drical electro-magnets are fixed ; the two circles of magnets consequently have 

 their poles opposite each other, with the disc and its circle of iron cores 

 revolving between them. The ends of the cores are terminated with iron 

 plates of a circular form, which answer the double purpose of retaining the 

 helices surrounding the cones in their places, and overlapping for a short dis- 

 tance the spaces between the poles of the electro-magnets. The closing of 

 the magnetic circuits of the electro-magnets and armatures for a short distance, 

 like the closing of the electric circuits for a brief interval at the point of no 

 current, has a marked influence on the power of an electro-magnetic induction 

 machine, both contrivances conspiring simultaneously to maintain the mag- 

 netic intensity of the electro-magnets during the rise and fall of the magneto- 

 electric waves transmitted through the helices. With the Gramme machine 

 much progress has been made in detail. One of the improvements, by 

 Mr. Robert Sabine, C.E., tends to add mechanical, and somewhat of electrical, 

 strength to the apparatus. Instead of the cumbrous magnets employed by 

 the inventor, Mr. Sabine proposes to substitute magnets placed parallel to 

 the coil (see Figs. 3 and 5 of our article on " Magnetic Illumination " in the 

 July number of this Journal) and united at their similar poles by transverse 

 bars of soft-iron. The magnetic polarity of these bars follows precisely the 

 Faradian lines of force, and the true pole appears to be situated in, or rather 



vol. in. (n.s.) 4 B 



