?o8 



NA TURE 



{July 26, 1888 



of the influence machines which I have present, and, in doing 

 so, I must ask a moment's leave from the subject of my lecture 

 to show you a small machine made by that eminent worker, 

 Faraday, which, apart from its value as his handiwork, so 

 closely brings us face to face with the imperfect apparatus 

 with which he and others of his day made their valuable 

 researches. . 



The next machine which I take is a Holtz. It has one plate 

 revolving, the second plate being fixed. The fixed plate, as you 

 see, is so much cut away that it is very liable to breakage. 

 Paper inductors are fixed upon the back of it, while opposite the 

 inductors, and in front of the revolving plate, are combs. To 

 work the machine (1) a specially dry atmosphere is required ; (2) 

 an initial charge is necessary ; (3) when at work the amount of 

 electricity passing through the terminals is great ; (4) the direction 

 of the current is apt to reverse ; (5) when the terminals are 

 opened beyond the sparking distance the excitement rapidly dies 

 away ; (6) it does not part with free electricity from cither of 

 the terminals singly. 



It has no metal on the revolving plates nor any metal 

 contacts ; the electricity is collected by combs which take the 

 place of brushes, and it is the break in the connection of this 

 circuit which supplies a current for external use. On this point 

 I cannot do better than quote an extract from p. 339 of Sir 

 William Thomson's " Papers on Electro-statics and Magnetism," 

 which runs : — " Holtz's now celebrated electric ^machine, which 

 is closely analogous in principle to Varley's of i860, is, I believe, 

 a descendant of Nicholson's. Its great power depends upon the 

 abolition by Holtz of metallic carriers and metallic make-and- 

 break contacts. It differs from Varley's and mine by leaving the 

 inductors to themselves, and using the current in the connecting 

 arc." 



In respect to the second form of Holtz machine I have very 

 little information, for since it was brought to my notice nearly six 

 years ago I have not been able to find either one of the machines 

 or any person who had seen one. It has two disks revolving in 

 opposite directions ; it has no metal sectors and no metal contacts. 

 The "connecting arc circuit" is used for the terminal circuit. 

 Altogether I can very well understand and fully appreciate the 

 statement made by Prof. Holtz in Uppenborris Journal of May 

 1881, wherein he writes that " for the purpose of demonstration 

 I would rather be without such machines." 



The first type of Holtz machine has now in many instances 

 been made up in multiple form, within suitably constructed glass 

 cases, but when so made up great difficulty has been found in 

 keeping each of the many plates to a like excitement. When 

 differently excited, the one set of plates furnished positive 

 electricity to the comb, while the next set of plates gave 

 negative electricity : as a consequence no electricity passed the 

 terminals. 



To overcome this objection, to dispense with the dangerously 

 cut plates, and also to better neutralize the revolving plate 

 throughout its whole diameter, I made a large machine having 

 twelve disks 2 feet 7 inches in diameter, and in it I inserted 

 plain rectangular slips of glass between the disks, which might 

 readily be removed ; these slips carried the paper inductors. 

 To keep all the paper inductors on one side of the machine to a 

 like excitement, I connected them together by a metal wire. 

 The machine so made worked splendidly, and your late Presi- 

 dent, Mr. Spottiswoode, sent on two occasions to take note of 

 my successful modifications. The machine is now ten years old, 

 but still works splendidly. I will show you a smaller-sized one 

 at work. 



The next machine on which I make observations, is the Carre. 

 It consists essentially of a disk of glass which is free to revolve 

 without touch or friction. At one end of a dicmeter it moves near 

 to the excited plate of a frictional machine, while at the opposite 

 end of the dicmeter is a strip of insulating material, opposite 

 which, and also opposite the excited amalgam plate, are combs 

 for conducting the induced charges, and to which the terminals 

 are metallically connected ; the machine works well in ordinary 

 atmosphere, and certainly is in many ways to be preferred to the 

 simple frictional machine. In my experiments with it I found 

 that the quantity of electricity might be more than doubled by 

 adding a segment of glass between the amalgam cushions and 

 the revolving plate. The current in this type of machine is 

 constant. 



The Voss machine has one fixed plate and one revolving plate. 

 Upon the fixed plate are two inductors, while on the revolving 

 plate are six circular carriers. Two brushes receive 'the first 



portions of the induced charges from the carriers, which portions 

 are conveyed to the inductors. The combs collect the remaining 

 portion of the induced charge for use as an outer circuit, while 

 the metal rod with its two brushes neutralizes the plate surface 

 in a line of its diagonal diameter. When at work it supplies a 

 considerable amount of electricity. It is self-exciting in ordinary 

 dry atmosphere. It freely parts with its electricity from either 

 terminal, but when so used the current frequently changes its 

 direction, hence there is no certainty that a full charge has been 

 obtained, nor whether the charge is of positive or negative 

 electricity. 



I next come to the type of machine with which I am more 

 closely associated, and I may preface my remarks hy adding that 

 the invention sprang solely from my experience gained by con- 

 stantly using and experimenting with the many electrical machines 

 which I possessed. It was from these I formed a working 

 hypothesis which led me to make the small machine now before 

 you. The machine is unaltered. It excited itself when new 

 with the first revolution. It so fully satisfied me with its 

 performance that I had four others made, the first of which I 

 presented to this Institution. Its construction is of the simplest 

 character. The two disks of glass revolve near to each other, 

 and in opposite directions. Each disk carries metallic sectors ; 

 each disk has its two brushes supported by metal rods, the rods 

 to the two plates forming an angle of 90° with each other. 

 The external circuit is independent of the brushes, and is formed 

 by the combs and terminals. 



The machine is self-exciting under all conditions of atmosphere, 

 owing probably to each plate being influenced by, and influencing 

 in turn its neighbour, hence there is the minimum surface for 

 leakage. When excited, the direction of the current never 

 changes ; this circumstance is due probably to the circuit of the 

 metallic sectors and the make-and-break contacts always being 

 closed, while the combs and the external circuit are supple- 

 mental, and for external use only. The quantity of electricity 

 is very large and the potential high. When suitably arranged, 

 the length of spark produced is equal to nearly the radius of the 

 disk. I have made them from 2 inches to 7 feet in diameter, 

 with equally satisfactory results. 



I have also experimented with the cylindrical form of I he 

 machine ; the first of these I made in 1882, and it is before you. 

 The cylinder gives inferior results to the simple disks, and is 

 more complicated to adjust. You notice I neither use nor re- 

 commend vulcanite, and it is perhaps well to caution my hearers 

 against the use of that material for the purpose, for it warps with 

 age, and when left in the daylight it changes and becomes useless. 



I have now only to speak of these larger machines. They are 

 in all respects made up with the same plates, sectors, and brushes 

 as were used by me in the first experimental machines, but for 

 convenience sake they are fitted in numbers within a glass case. 



This machine has eight plates of 2 feet 4 inches diameter ; it 

 has been in the possession of the Institution for about three years. 



This large machine, which has been made for this lecture, has 

 twelve disks, each 2 feet 6 inches in diameter. The length of 

 spark from it is 13! inches. 



During the construction of the machine every care was taken 

 to avoid electrical excitement in any of its parts, and after its 

 completion several friends were present to witness the fitting of 

 the brushes and the first start. When all was ready the terminals 

 were connected to an electroscope, and the handle was moved, 

 so slowly that it occupied thirty seconds in moving one half 

 revolution, and at that point violent excitement appeared. 



The machine has now been standing with its handle secured 

 for about eight hours ; no excitement is apparent, but still it may 

 not be absolutely inert ; of this each one present may judge, 

 but I will connect it with this electroscope, and then move the 

 handle slowly, so that you may see when the excitement com- 

 mences and judge of its absolutely trustworthy behaviour as an 

 instrument for public demonstration. I may say that I have 

 never under any condition found this type of machine to fail in 

 its performance. 



I now propose to show you the beautiful appearances of the 

 discharge, and then in order that you may judge of the relative 

 capabilities of each of these three machines, we will work them 

 all at the same time. 



The large frictional machine which is in use for this com- 

 parison is so well known to you that a better standard could not 

 be desired. 



In conclusion I may be permitted to say that it is fortunate I 

 had not read the opinion of Sir William Thomson and Prof. 



