Oct. 13, ibSi] 



NA TURE 



569 



dent of climate and season, and furnishing him with a pouer of 

 producing new varieties. 



Before electro-horticulture can be entertained as a practical 

 process it would be necessary ho .\ ever to | rove its cost, and 

 my experiments of last winter were in part directed towards 

 that object. Where water-power is available, the electric light 

 can be produced at an extremely moderate cost, comprising car- 

 bju electrodes, and wear and tear of and interest upon apparatus 

 and machinery employed, which experience elsewhere has al- 

 ready shown to amount to td. per hour for a light of 5000 

 candles. The personal cm-rent a'tention requisite in that case 

 consists simply in replacing the carbon electro;les every six or 

 eight hours, which can be done without appreciable expense by 

 the under-gardener in charge of the fires of the greenhouses. 



In my case no natural source of power was available, and a 

 steam-engine had to be resorted to. The engine of 6 normal 

 horse-power which I employ to work the two electric lights of 

 5000 ciudle-power each, consumes 56 lbs. of coal per hour (the 

 engine being of the ordinary high-pressnre type), which, taken 

 at 20). a ton, w-ould amount to tJ. or to 31/. per light of 5000 

 candles. Uut against this expenditure has to be placed the 

 saving of fuel effected in suppressing the stoves for heating the 

 greenhouses, the amount of which I have not been able to ascer- 

 tain accurately, but it may safely be taken at two-thirds of the 

 cost of coal for the engine, thus reducing the cost of the fuel per 

 light to id. per hour ; the total cost per light of 5000 candles 

 will thus amount to i>d. -I- \d. — "jd. per hour. 



This calculation would hold good if the electric light and 

 engine power were required during say twelve hours per diem, 

 but inasmuch as the light is not required during the daytime, 

 and the firing of the boiler has nevertheless to be kept up 

 in order to supply heat to the greenhouses, it appears that during 

 the daytime an amount of motive-pDwer is lost equal to that 

 emiJloyed during the night. 



In order to utilise this power I have devised means of working 

 the dynamo-machine also during the daytime, and of transmitting 

 the electric energy thus pro:Uiced by means of wires to different 

 points of the farm, where such operations as chalf-cutting, 

 swede-slicing, timber-sawing, and water-pumping have to be 

 performed. 



These objects are accomplished by means of small dynamo- 

 machines pi. ice I at the points where power i- required for thee 

 various purposes, and which are in metallic connection with the 

 current-generating dynamo-machine near the engine. The con- 

 necting wires employed consist each of a naked strand of copper 

 wire supported on wooden poles or on trees without the use of 

 insulalo.-s, whilst the retur'n-circuit is effected through the park- 

 railing or wire fencing of the place, which is connected witli 

 Ijoth transmitting and working machines by means of short 

 pieces of connecting « ire. In order to insure the metallic con- 

 tinuity of the wire fencing, care has to be taken wherever there 

 are gates to solder a piece of wire, buried below the gate, to the 

 wire fencing on either side. 



As regards pumping the water, a 3-horse-power steam-engine 

 was originally used, working two force-pumps of 3j-inch 

 diameter, making thirty-six double strokes per minute. The 

 same pumps are still employed, being now worked by a dynamo- 

 machine weighing 4 cwt. When the ci^terns at the h use, the 

 gardens, an I the fann require filling, the pumps are started by 

 simply turning the commutator at the engine station, and in like 

 manner the mechanical operations of the farm aheady referred 

 to are accompli-hed by one and the same prime mover. 



It would be difficult in this in-tance to state accurately the 

 percentage nf power actually received at the distant station, but 

 in trying the same machines under simdar circumstances of 

 resistance with the aid of dynamometers, as much as 60 per cent, 

 has been realised. 



In conclusion, I have plea nre to state that the working of the 

 electric light and transmi-sion of power for the various opera- 

 lions just named are entirely under the charge of my head- 

 gardener, Mr. Buchanan, a.ssisted by the ordinary staff of 

 under-gardeners and field-labourer.s, who proba' ly before never 

 heard of the power of electricity. 



Electric transmis ion of power may eventually be applied 

 also to thrashing, reaping, and ploughing. These objects are at 

 the present time accomplished to a large extent by means of 

 portable steam-engines, a class of engine which has attained a 

 high degree of perfection ; but the electric motor presents the 

 great advantage of lightness, its weight per horse-power being only 

 2 cwt., whilst the weight of a portalJe engine with its boiler 



filled with water may be taken at 15 cwt. per horse-power. More- 

 over, the portable engine requires a continuous supply of water 

 and fuel, and involves skilled labour in the field, nhil-t the 

 electrical engine receives its food thn.ugh the wire (or a light 

 rail upon which it may be made to m jve about) fi'om the central 

 station, w here power can be produced at a cheaper rate of ex- 

 penditure f r fuel and labour than in the field. The use of 

 secondary batteries may also be resorted to with advantage to 

 store electrical energy when it cannot be utilised. 



In thus acconplihing the work of a farm from a central- 

 power station, considerable savings of plant and labour mry be 

 effected ; the engine-power will be chicfiy required for day work, 

 and its night Wurk for the purposes of electro-horticulture will 

 be a secondary utilitation of the est;ibli»hment, involvin; little 

 extra expense. At the same time the means ore provided of 

 lighting the hall and shrubberies in the most perfect manner, and 

 of producing effec's in landscape gardening that are strikingly 

 beautiful. 



THE ELECTRICAL DISCHARGE, ITS FORMS 

 AND ITS FUNCTIONS' 

 II. 

 A MONG the various circumstances which combine to determine 

 •^~*- the character of the discharge, one of the most important is 

 the size of the negative terminal. And in this respect, as well as 

 in others, tlie negative difiVrs fundamentally from the positive. 

 If the negati/e be small, not so much in comparison with the 

 positive as in alisolute magnitude, and 1 erha; s al o in reference 

 to the diameter of the tube, the tube will offer great "resist- 

 ance," as it is termed, to the passage of the discharge. On the 

 other hand, if the negative be large, the discharge passes with 

 comparative ease. In the first case, even when the discharge 

 passes, stria: are formed only with difficulty, if at all ; in the 

 second tl-.ey are readily formed. This may ea ily be shown by 

 using a tube with one small and o.ie large terraina', which can 

 be used alternately as positive and as negative ; or by a tube 

 having a negative terminal of variable length. 



The same dependence of striation upon the size of the nega- 

 tive may be shown in the case of a tube with a negative terminal 

 of barely suffrcient size. In this case, if the tube be touched by 

 the hand (an operation which, as will be hereafter explained, is 

 equivalent to enlarging the negative), stria; will be brought out 

 clear and distinct, while without this a'Sistance they appear 

 only in a confued and irregular manner. 



Other characteristic features of the negative terminal would 

 deserve our attention if time permitted. Thus, the well-known 

 phenomer a of the so-called " Holtz tul e" (or tulie divided into 

 compartments by diaphragms furnished with narrow pipes 

 leading from one c mipartn e .t to the next, and all pointed in 

 one direction), show that a small aperture wdl serve as a nega- 

 tive, t)ut not as a positive terminal. This property has been 

 generalised by G ildstein, w ho, using as a negative terminal a 

 cylinder of non-conducting substance pierced with fine holes, 

 reproduces all the phenomena sppertaining to an ordinary 

 metallic negative. 



And, even apart from the phenomena of vacuum tubes, it 

 would not be difticult to adduce instances shoeing the import- 

 ance of the size of the negative terminal in electrical discharges 

 generally. Of these I will now mention only the latest. In 

 making some modifications of Plante's battery M de Pozzer has 

 found that, if the negative electrode be made of a plate of lead 

 of half a millimetre in thickness, and the positive of one of two- 

 thirds of a millimetre, but the for.r.er doulile the size of the 

 latter, great advantage arises from the greater size of the 

 negative. The di-charge fr^m a battery ha\ing a negative double 

 as large as the positive la-ted, on r.n average of several experi- 

 ments, for an hour ; while that from a 1 attery, m which tie 

 sizes of the electrode were reversed, lasted only half an hour. 

 The effect of a battery with electrodes of equal size appears to 

 have been interirediate to that of the two others. 



From ihese phenomena, and es lecia'ly from those of the 

 moviig terminal, as well as from other considerations, it appears 

 that the general confiiuratirm of the discharge is mainly deter- 

 mined at the negative terminal. 



In order, h.jwever, to experiment wiih any hof e of progress 



^ A Lecture delivered before the British Association at York on September 

 5, 1881, by Will.am Spottiswoode, D C.L., LL.D., President of the Royal 

 Society. Continued from p. 551. 



