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Nov. 18, 1881. THE ENGINEER. ES61 THE PARIS ELECTRICAL EXHIBITION. mutator consists of a cast brass ring somewhat resembling ence; or, in other words, that the dimensions of these rods half a split key-ring, as shown in side view Fig. 6. Two have been arrived at by the process of trial and failure. No. XIV. of these rings fit into each other, and resemble a complete key- All these facts considered, the matter seemed one of no In our last impression we described Hopkinson ’s ring, with, however, the two parts insulated by vulcanised small mechanical interest. For apart from the importance electrical hoist, exhibited by Messrs. Latimer, Clark, Muir- fibre from each other. This compound ring, Fig. 4, is fitted of these rods and the desirability of supplying a theoreti head, and Co. The same firm exhibited a dynamo machine ! uPon a small drum of wood with twelve equidistant holes cally derived formula in place of empirical rules, the expe designed by Mr. Andrews. The object of the designer is P!e!'cecl thr0”«h as in 6> (w“ch slltTs a rience of the fitness of these rods has been so ample that ° J . .. ., , , ,.J ... , ... plete commutator for one section of the armature, lhe as soon as we are in a position to calculate the stresses in to obtain simplicity of construction without sacrificing twelve ends from the six pairs of coils are passed through their material they furnish a very important test as to the efficiency. Fig. l shows a perspective view, and Fig. 2 a the twelve holes in the wood as each commutator is slipped factor of safety for such parts of machinery. Thus,it appears section of a 6-light machine, which, we understand, will upon the spindle. The ends for each commutator are con- that while a rule has been laid down that a certain stress is be shown at the forthcoming Exhibition at the Crystal nected to their respective parts by the small boss cast the greatest which the iron in any important part of a Palace. The field magnets are built up by means of two upon each ring. As each commutator is placed upon the machine should bear, these very important parts have castings, which form two complete horseshoe magnets, the spindle of the armature, the connecting boss is brought been unwittingly allowed to bear, and have borne safely, like poles of which are combined in one casting. The one-twelfth in advance of its neighbour, in order that the half as much again as that given by the rule. That the faces of these magnets are presented to the armature, same end shall not pass into two commutators. Thus the stress in these rods may be as great as appeared from and the extremities are connected together by the _ ribs ends of all the coils pass through the wood of all the com- theoretical consideration, or, at least, that they are the outside. Pound each of the poles is placed a coil of mutators, but they can only become electrically connected parts of the engine which first give way when an undue No. 10 wire, which is first wound on a wrought iron enve- with their parts, which renders the connection very speed is attained, has been confirmed by the records of lope, and then slipped upon the pole piece with the enve- simple. From this it will be evident that the pair of railway accidents. Shortly after the first investigations lope. In_ consequence of the large mass of iron consti- brushes for each commutator must be side by side and on were made, a train having on it three similar coupled FIC . L F I G .2 FI C 4- ■jjffisMijgggS iiiili iriiiiiiiiiiiiil gw 1 m FIC 6 //////////////. FIC 5 mmr, pilil g;21 1 I 'm m mr ml#|ifK - mwm a ::s J MV B HP lllllllllilllllllllllllll FI C 3 (fjjlillHIIJ IIII w II 11 @0 :■!!* I 1 IB mu U 19® mW//////////////A1 iiiHiiiHUiyiiitiiiiiifiHiiiinyjiuniig) m........ i!1 ±'1 _ 11' "i ''I ANDREWS’ DYNAMO MACHINE. tuting the poles, there is a probability of a pole of the top, this position giving great facilities for adjustment. engines ran away down an incline, the brakes being over opposite ■character presenting itself in the centre, and It will be seen from this description that the arrangement powered, and eye-witnesses described how the first to prevent this the extreme part of each pole is cast followed admits of six circuits, one of which is used to symptom of disaster was the flying off of the coupling rods hollow. excite the field magnets. The remaining five circuits can from one of the engines, those from the others following be connected as required for the particular purposes in immediately after. In 1878 attention was called to these FIG. 7. hand, thus can be used as five separate circuits, or quan facts at a meeting of the Manchester Literary and Philo titatively, or in series as desired. sophical Society, and they excited the interest of Dr. Joule, fll Besides the machine Mr. Andrews has designed an who has kindly sent the author published accounts of electric light indicator. This indicator is shown by Messrs. several instances of the failure of these rods in cases of Clark, Muirhead, and Co. It takes the place in the high speeds. Amongst these was the following extract electric light circuit that the ordinary galvanoscope does from a letter published in the Manchester Courier. The in a telegraphic circuit. It indicates at all times whether accident occurred on the Cheshire line from Manchester a current is circulating, and to within half-a-veber its N9I N92 to Liverpool, on which the speeds are very high. amount. Fig. 7 shows a board of such indicators The author of the letter has clearly used the term ML arranged for four circuits. Fig. 8 shows the construction connecting rod in the sense of coupling rod. “ Shortly K of the indicator. It mainly consists of a coil of wire after we had passed one of the small stations on the V wound on a brass box. Fitted into this, but removable way, and before reaching Warrington, the connecting rod from it, are two brass pieces connected together by the of the engine, or some other material portion of that part fixed half of an iron core. The other half core is hinged N°3 N°4 of the mechanism, became broken, and flew off with such ImiitiHmiiituimil muni! at its centre, so that the combination somewhat resembles force as to strike the embankment on the near side, and a pair of scissors. To the movable half-core is attached thence rebound with terrible power into the window of an index, which by means of a scale indicates the quan one the third-class carriages immediately behind, com m m tity of current passing. The magnet being made entirely pletely smashing in the woodwork, as well as all the glass, of soft iron, and there being no permanent magnets to the great danger of one or more passengers within, but employed, there is no liability of the constant, which may who escaped uninjured. I was a passenger on another The armature consists of a long cylinder with radial be taken once for all, being altered by strong magnetic occasion, on the same journey, when the connecting rod projections, round which coils of wire are wound. The influence. The instrument is altogether very simple and snapped in two, and the two pieces continued to whirl armature is shown in section in Fig. 2, and in elevation in hardly liable to get out of order, and will no doubt be round until the train could be stopped, to the great risk Fig. 3. The cylinder is built up of a number of stamped found useful in all electric light work. of driving the engine and carriages from the metals. And stars of No. 16 B.W.G., which are separated by tissue I have heard it said that accidents of a similar kind have occurred on other occasions. ” THE LIMITS TO SPEED. The theory of these rods has been taught in the engi neering classes at Owen’s College for several years, but its By Professor Osborne Reynolds , M.A., F.R.S first appearance in print seems to have been in a letter in No. II. The Engineer of May 27th, 1881, signed “ S. R.,” dated m To obtain an idea of the effect of accelerations, we may Manchester, May 11th ; and more fully in an article which take an instance of a moving machine, and supposing its appeared in The Engineer , of Sept. 9th, 1881. Leaving speed to increase, consider which of its parts would give what we may call the swinging forces out of considera way first. The locomotive seems to afford the best tion, the coupling rods are designed to withstand certain example. Imagine, then, a locomotive to be started down forces which cannot exceed a definite amount. This a long incline with the steam fully on ; what part of the amount may be estimated for each particular case. The machine would give way first 2 In the case of an engine utmost one rod can be called upon to do is to turn one with its wheels coupled, the question may be answered pair of wheels against the whole friction between the with certainty. The coupling rods would be thrown off wheels and the rail, which latter may be sanded. In such Although perhaps not generally known, this has been a case, F, the coefficient of friction, would be about ‘3.

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