Sept. II, 1879] 



NATURE 



467 



were due to the sun's liglit falling upon the compound of carbon 

 and rendering it visible, in the same way that light renders the 

 moon, the planets, and other opaque objects visible, the vapour 

 of carbon being opaque in reference to the particular rays, which 

 appear as bright lines in its spectrum. 



On Improvements in Dynamo-Ehctric Machines, by W. Ladd. — 

 My object in this communication is to describe in a few words 



Westor/s Dyiu -il^u.-iiC Machine. 



the peculiarities and improvements in the cor.straction of Weston's 

 dynamo-eIe:tric mr.chine. 



The Field Magnets. — The general appearance and arrangement 

 of which may be seen in the illustration. The pole pieces are 

 composed of iron plates, placed side by side in a mould, but 

 separated a uniform distance from each other. The iron mag- 

 nets, on which the wire is to be wound, are cast on to_ "lugs," 

 or projections on the ends of the plates. The two cast-iron ends 

 and uniting plates form one magnet ; the upper and lower mag- 

 nets are alike, and when joined together by the perforated 

 vertical supports, the inner curved edges of the field plates 

 embrace about two-thirds of the circle in which the armature 

 is made to revolve. 



The arinature is built up of plates which are somewhat like a 

 cogged wheel in shape (see illustration). These plates are 

 stamped out of sheet-iron, and when mounted on the shaft are 

 separated from each other at a uniform distance ; the radial pro- 

 jections are then arranged in lines, so that the whole forms _a 

 very broad cogged wheel, or cylindrical structure having longi- 

 tudinal grooves, with transverse spaces at regular distances. The 

 longitudinal grooves are for carrying the wire, and it will be ob- 

 served from the nature of the structure that the wire lies vet 

 channels three sides of which are iron ; so that the mutual effect 

 upon each other is increased as much as possible. The ends of 

 the wires are connected to the field magnets and commutator in 

 much the usual way, the currents travelling in one direction only. 

 The commutator is fitted on a portion of the shaft which projects 

 beyond the bearings. This admits of its easy removal and a new 

 one being replaced in three minutes. 



Another important feature in the construction is the arrange- 

 ment for ventilation ; the separation between the pole plates of the 

 field magnets, the perforation in the vertical supports of the 

 magnets, and the light frame-work of the armature, are all for 

 this purpose. The air enters the centre of the armature, and is- 



Armature of Weston's Dynamo Electric Machine 



driven out between the layers of wire through the spaces formed 

 by the separated plates of the armature and the field magnets, 

 and thus prevents any part from becoming unduly heated. 



Machines of this description are made of various sizes and 

 strengths, and give from one to sixteen lights in single circuit. 



On the Direct Motion of Periodic Comets of Short Period, by 

 Prof. H. A. Newton. — The periodic comets of short period, 

 that is, the comets certainly seen at two returns, twelve or fifteen 

 in number, have, all but one or two, small inclinations to the 

 ecliptic ; Halley's comet is an exception, being nearly retrc^ade 

 in motion. Perhaps we may add the comet with which the 

 November or Leonid meteors are connected (1866, I), since it is, 

 I think, almost certainly identical with the comet of 1836, and 

 has an inclination of about 163°. 



The direct motion of the periodic comets seems to give them 

 a peculiar relation to the solar system, even suggesting for them 

 an origin common in some way w ith the origin of the planets. 

 The other comets apparently come to us from outside the solar 

 system, and if in any cases they are permanent members of the 

 solar system, they have become such by the perturbations of the 

 planets. Can it be that such perturbations have also forced the 

 periodic comets into their present orbits ? 



The ordinary perturbating forces are small, and would almost 

 as frequently increase as diminish the inclination of a comet's 

 orbit. To every comet passing on one side of a planet, and so 

 having its inclination diminished, there should be among an in- 

 definitely large number of comets a .second comet (.assing on a 

 symmetrically opposite side, and having its inclination increased, 

 liut if we state the question properly, we get a different answer. 

 If an indefinitely great number of comets approach and pass a 

 large planet, and if the directions and lines of motion are uni- 

 formly distributed, some of those comi::^ near to the planet will 

 be turned into orbits of short period. Considering only the 

 orbits thus affected, w ill they have in general small inclination ? 

 I find that they will, and that therefore we are not required, be- 

 cause of their different motions, to consider the periodic comets 



of short period as difterent in genesis from those of long period, 

 or from those having parabolic orbits. 



The conclusion suggests the possibility of a common outside 

 origin to the periodic comets and the asteroids. It also suggests 

 the possibility of an outside origin for the matter that makes up 

 the zodiacal light, since it would explain the near coincidence of 

 the plane of this mass with the ecliptic, notwithstanding its out- 

 side origin. 



If, in addition, we may admit a like origin for the 'satellites, 

 and even for some of the smaller planets, we are rid of the diffi- 

 culty that seems to me insuperable, of .supposing, as is usually 

 done, that the very small bodies become solid from a nebulous 

 state in the immediate presence of the sun and large planets. 



On Self-acting Intermittent Syphons and the Conditions which 

 Determine the Commencement of their Action, by Rogers Field, 

 B.A. — In an extensive series of experiments which the author 

 tried some years ago on syphons, with their outer legs dipped in 

 water, he was much puzzled by finding that the quantity of water 

 necessary to put a syphon of given size into action varied in the 

 most unaccountable way at different times. The only difference 

 that could be perceived between the cases in which the syphon 

 started and those in which it did not start was, that in the former 

 case air-bubbles escaped freely at the mouth of the syphon, 

 whereas in the latter case, under apparently the same conditions, 

 very few bubbles came out. At last the idea suggested itself of 

 making a portion of the syphon in glass so as to see what was 

 going on inside the pipe, when the course of the irregularity was 

 at once discovered. Sometimes the water which ran over the 

 bend adhered closely to the sides of the pipe, at other times a 

 portion of it would fall more or less clear of the sides. When 

 the water adhered to the sides it produced very little effect in 

 displacing the air, so that only a small quantity of air was driven 

 through the water at the mouth of the syphon. When on the 

 other hand the water fell clear of the sides, it produced a great 

 effect in displacing the air, and large bubbles of air at once 

 escaped from the mouth of the syphon. 



