Dec. 15, 



• KNOWLEDGE • 



471 



shown in the figure, and the distance between these ter- 

 minals can be varied at pleasure by sliding them through 

 the balls which are attached to the inner coatings of the 

 two cylindrical Leyden jars by which the charge is ac- 

 cumulated and the discharge intensified. E is a vertical 

 bar of brass, carryin;: at each end a comb, directed towards 

 the rotating plate, as well as a pairof metallic brushes similar 

 to F and F, and which also in their turn make momentary 

 contact with the metallic buttons as they pass beneath 

 them. 



The machine is a step far in advance of anything pre- 

 \-iously produced, although it is somewhat similar in 

 principle to Varley's electrostatic inductive multiplier. 



A small initial charge is imparted to the machine in 

 some as yet undetermined way. It may be due to the 

 friction of the metallic brushes with the studs or buttons ; 

 or, on the other hand, it is possible that the various parts 

 of the machine Ijefore starting are in slightly different 

 electrical conditions. Whichever of these hypotheses is 

 correct, a small charge of, we will say positive, electricity 

 collects on one of the pairs of discs, on the fixed plate, and 

 from this, as a nucleus, brilliant discharges may be obtained. 

 To analyse the action of the machine, we will assume that 

 we start with a stud, as being typical of the others, imme- 

 diately after it has passed the bent arm, H, on the left, and 

 that the corresponding side of the fixed plate has the small 

 positive charge above referred to. As the stud passes 

 before the charged disc, electricity is induced on it, the 

 inner surface becoming negative, the outer receiving a 

 positi\e charge, which is collected by the horizontal comb 

 E', and passes thence along the brass rods to the discharge 

 terminal, C, and the inner coating of the Leyden jar, L, 

 The stud, in revolving, undergoes further induction, and on 

 arriving at the vertical comb, E (really not quite vertical, 

 but opposite the end of the paper^, a further withdrawal 

 of positive electricity takes place ; a considerable negative 

 charge, therefore, remaining. This the stud carries round 

 till it meets the brush of the bent arm on the right 

 side of the machine. By this means, a negative 

 charge is communicated to the pair of discs on the 

 right half of the fixed plate, the stud at the same 

 time becoming neutralised. It is then re-excited in 

 an exactly opposite manner to tliat previously ob- 

 served, negative being imparted to the horizontal 

 comb, E', and Leyden Jar, L', and likewise to the 

 lower of the two vertical combs. A positive charge is 

 collected by the bent arm, H, on the left, thereby increasing 

 the charge already collected on the corresponding pair of 

 discs. This action continuing, a large charge accumulates 

 on the fixed plate. It follows that if, by means of the 

 electricity collected through the bent arms, we increase 

 the inducing charges on the fixed discs, we shall obtain pro- 

 portionately increased charges in the horizontal collecting- 

 combs. Assuming that the discharging terminals (C G) are 

 in contact, there will obviously l)e an almost constant flow 

 of positive electricity in one direction and of negative in 

 the other. If, a few seconds after the working commences, 

 we separate the discharging terminals, a stream of sparks 

 may be obtained. The function of the vertical combs is, 

 as may be gathered from the alwve, an important one, their 

 duty being to relieve the studs of the free electricity 

 induced in them as they pass from the horizontal combs 

 towards the vertical. 



Viry little labour is required to work the machine, owing 

 mainly to the fact that practically none of the electricity is 

 generated by friction, the small amount of work performed 

 in turning the plate being almost entirely converted into 

 induced electricity. The machine works well in any atmo- 

 sphere, hot or cold, wet or dry — a very important point, 



considering the effect usually produced by the humidity of 

 the air. Every lecturer or student of electrical science 

 knows how difficult it is to generate static electricity 

 by the ordinary frictional machine when a few per- 

 sons are present in the room. As the result of 

 considerable experience with the Yoss, we can confidently 

 say that such difficulties need never be apprehended, while 

 a flow of sparks, 4 in. or more in length, can be relied upon 

 from a machine weighing less than 7 lb., and with a rotatmg 

 plate 10|in. in diameter. All the ordinary experiments 

 of static electricity can, of course, be performed, and wi- 

 are rarely able to so confidently recommend a commodity 

 as we can the Voss machine to all who desire to perform 

 electrical experiments with a minimum amount of trouble 

 and at a moment's notice. The machine is comparatively 

 a cheap one, and the English agents, ilessrs. F. E. Becker 

 i- Co., of Maiden-lane, Co vent-garden, are now manu- 

 facturing it in large numbers. 



^^ 



Ittttvi to tbr euitor. 



Onhi a small propftrtion of Lftters ivr.-i .fd can posfihly he iii- 

 gerted'. Corre.'>potide)its mvst not Ic ofeiuU-d, therefore, shoitld their 

 letters not appear. 



All Editorial communicatiotis should be addressed to the Editoe of 

 Knowledge ; all B^isiness commvnications to the Publishers, at the 

 Office, 74, Great Queen-street, W.C. If this is not attekded to, 



DELAYS ARISE FOE WHICH THE El>nOR IS SOT RESPONSIBLE. 



All Remittances, Cheques, and Post Office Orders should be made 

 payable to Hessrs. Wymas & Sons. 



The Editor is not responsible for the opinions of correspondents. 



No COMMrMCATIOXS ARE ANSWERED BY POST, EVEN THOCCH STAMPED 

 AND DIRECTED ENVELOPE BE ENCLOSED. 



" Let Knowledge grow from more to more." — Alfred Tennyson. 



SAXrRX'S RIXG. 



[656]— It may not be amiss to rectify a mistaken assumption of 

 Captain Noble, in his letter printed at p. 329 of Knowledge. The 

 " person to whom notice was sent hereof " was not Wallis, but Sir 

 Robert Moray— first President of the Royal Society. This appears 

 from William Dalle's letter to Oldenbnrcr, dated April 14, 1666, in 

 ^vhich he asks whether Sir R. Moniy has oonimnnicated his obser- 

 vation of the previous autnmn. 



I notice that throughout the correspondence in Knowledge the 

 place where Balle made his observations is printed Mainhead. This 

 is doubtless due to the mis-S]ieUiug in " Phil. Trans." It should be 

 JIamhead. There are two letters from Ballo in the arehives of the 

 Roval Society — both (as may be seen by the published " Catalofrtie 

 of the MS. letters in the possession of the Royal Society") dated 

 from JIamhead. The only instance in which the name is written 

 " Mainhead" is on a cutting attached by sealing->vax to thi< fly-leaf 

 of the first letter, but it is doubtful whether this is in Balle's 

 writing. 



It may interest ycur readers to know that there is a postscript at 

 the end "of Balle's letter of April 14, 1666, containing another figure 

 of Saturn. This figure has a dotted line across the sphere indicating 

 the shadow of the ring, but the ring itself shows no vestigi> of any 

 dividing line. This observation, however, was made only with a 

 twelve-foot gla.os. IIebiiebt Uix. 



Science Club, Savile-row, W. 



BRAIN TROUBLES. 

 [C.'T] — May I add a quota to the singular experiences of this 

 kind: I write a good deal by tits and starts. .\t intervals — not 

 very frequent — I catch myself omitting the first letter of some 

 words I As far as I hove casually observed, the graphical objec- 

 tion is at <i and p. Not thrice n year, iierhapsi. does this happen ; 

 but, when it does occur, I have occasionally to ro-wrile a note in 



