May 18, 1883.] 



o KNOWLEDGE ♦ 



295 



Fig. 1. 



in which the wall of Cyrillus has been intruded on by 

 Theophilus. 



Little or no detail is observable in Catherine when so 

 near the terminator, but the shape of the shadows cast 

 into its interior reveals that of the ridges and peaks 

 causing them. Cyrillus will be seen to be more trapezoidal 

 than circular, and the two mountains in its centre and the 

 conspicuous crater on its wall will at once arrest the eye. 

 Theophilus is the deepest crater in the moon, the walls 

 being in places 18,000 feet above the level of the bottom. 

 Its diameter is nearly G4 miles. Necessarily its sides are 

 brilliantly illuminated by the rising sun when the interior 

 is plunged in the blackest night, and at about the fifth day 

 of the moon's age it may be seen projecting beyond the 

 terminator into the darkness of the seemingly surrounding 

 sky as a brilliant ring. Sharp-sighted people can detect 

 this without any optical aid. 



2,000 candle-power each, the weight of the machine 

 being 2,200 lb. The inducing or field magnets consist 

 of four massive pieces of iron, wound round with 



THE BRUSH DYNAMO-ELECTRIC 

 MACHINE. 



URGED by several correspondents, we purpose describing 

 a few of the more important dynamo-electric machines 

 adopted by the various electric lighting companies. The 

 Gramme has been before the public about twelve years, and 

 for this reason we refrain from giWng a detailed description 

 of it here. Nevertheless, it is only right that we should 

 remind our readers that it was M. Gramme who first 

 rendered the conversion of mechanical power into electricity 

 practical. His machine may be said to bear the same rela- 

 tion to dynamos that the Daniell cell does to galvanic 

 batteries, each being the first practical form, and still, for 

 many purposes, the most efficient. 



The Brush machine is one which has during the past 

 two years commanded a great deal of attention, and what- 

 ever may be said of the various transactions in connection 

 with it, it can scarcely be denied that it has done some 

 really good work, and that, for arc lighting on a large scale, 

 it is capable of standing its ground with any in the field. The 

 machine is made in various sizes, Fig. 1 representing the 

 one used to supply the current for sixteen arc lights, of 



F.C. 2 



stout copper wire (No. 10 gauge). Two of these (B B) are 

 shown in the figure, the other two being exactly behind 

 them. The inner face of each of the iron cones is flattened 



out so as to extend nearly half way round the circle formed 

 by the armature (A). By reference to Fig. 4, which is a 

 typical horizontal section, it will be seen that the field 

 magnets are joined together in pairs, M M and M^ M', by 



