PLATE MACHINES.] 



TJNDULATORY FORCES. ELECTRICITY. 



171 



In a modification of the plate machine invented by 

 Mr. Winter, an arm, extending to a height of three feet 

 above the conductor, is placed, which, by its inductive 

 effect, has the power of increasing the length and inten- 

 sity of the spark to an astonishing degree. 



Plate machines are made of various sizes. Indeed, we 

 hav3 experimented with them from those of one foot to 

 one of seven feet diameter, of glass surface. The latter 

 instrument may be seen at the Royal Polytechnic, Re- 

 gent-street, London ; and from it we have obtained 

 sparks from six inches to two feet in length, depending 

 on the dryness of the atmosphere and other circum- 

 stances, to which we shall have to allude. One of still 

 larger size was daily used at the Panopticon, Leicester- 

 square, some years ago. It had a plate ten feet in dia- 

 meter, and was furnished with double rubbers and con- 

 ductors. It is now in private hands, and is the finest 

 specimen of a plate electrical machine yet produced. 



We may here give a caution to those intending to 

 purchase an instrument of this kind. The quality of 

 glass used very materially affects the results which can 

 be obtained. On one occasion, a twelve-inch plate which 

 we possessed was cracked by being over-heated. On 

 fitting the machine with a new plate, we found that we 

 could not obtain anything like so good a spark as from 

 that previously used. This was owing to a peculiar 

 " greasiness" on the new glass. Some plates will attract 

 moisture more than others ; which, of all things, is most 

 to be avoided in electrical experiments. The only gene- 

 ral rule we can give is, that the more highly polished the 

 glass, the fitter it is for the purposes of the electrician. 

 Plates having specks, streaks, or spots on their surfaces, 

 should be rejected ; and the rim of the glass should have 

 ax complete a polish as the flat surface. It is, also, of 

 'tmost importance, that the spindle which holds the 

 plate, and on which it turns, should bo fixed exactly in 

 the centre. If this be not attended to, there will be an 

 unequal pressure on the glass as it revolves, and risk of 

 fracture will be inevitable. 



Attention should also be paid to the construction of 

 the clamp holding the rubbers, and to the mode in which 

 the conductor is fixed on its supports, especially il placed 

 on one glass rod only, as is frequently the case. 



Before proceeding to the description of other forms 

 of electrical machines, we will give directions for the 

 management of those we have illustrated and explained ; 

 and we must impress on the mind of our readers, the 

 necessity of a strict adherence to the precautions, .to., 

 we shall mention, if they would obtain successful results 

 iii tlieir electrical studies. 



Some old silk handkerchiefs should be provided, which 

 are much to be preferred to any other material, because 

 silk does not afford fine fibres, as do cotton and linen. 

 A few such fibres, if they get on the glass surface, adhere 

 to it with great pertinacity, and have an astonishing 

 effect in dispersing electricity. 



The cylinder or plate machines are prepared for use as 

 follows : 



1. Wipe the whole machine, glass, legs, handle, and 

 font, by means of a warm, dry handkerchief, so as to re- 

 move all dust or dirt which may have accumulated on its 

 surface 



2. Wash the cylinder or plate by means of a rag 

 moistened with spirits of wine having first loosened or 



<ved the rubbers. This will cleanse away all hard 

 matter which may have remained from previous experi- 

 ments. The cylinder or plate is then to be rubbed with 

 a dry handkerchief, until it has a high polish, and is quite 

 free from every extraneous subst.i 



3. The rubbers should be carefully cleaned, if they have 

 been previously in use, especially if any hard amalgam 

 has been left on their surface. The more evenly they 

 press on the glass, the greater will be the amount of elec- 

 tricity which will be produced. 



After thus cleansing them, they may be slightly 

 smeared with good tallow, and the amalgam is then to 

 be spread evenly over the surface by means of a palette- 

 knife. The amalgam is made by pounding together in a 

 mortar one ounce of zinc shavings, with two ounces of 



clean mercury. The two metals will soon combine ; and 

 the amalgam should be kept in a box or bottle, out of 

 the air, because it would soon otherwise become oxidised 

 and spoilt. 



4. The rubbers having been thus amalgamated, are to 

 be replaced and screwed up, so as to press evenly and 

 firmly on the surface of the cylinder or plate ; the silk flap 

 being thrown back, lest it should become soiled. The 

 handle of the machine is now to be turned gently, and 

 the grease, <fcc., must be wiped off the machine until the 

 rubbers no longer soil the surface. The silk flaps may 

 now be placed over the glass, and the machine is ready 

 for use. 



5. As, however, all glass and metal surfaces receive a 

 coating of moisture on being used in a room of higher 

 temperature than their own, it is advisable to warm the 

 whole machine before a fire, until its temperature exceeds 

 that of the surrounding atmosphere. By this, all chance 

 of the deposition of moisture is prevented. A silk hand- 

 kerchief should be thrown over the machine whilst it is 

 being warmed, so as to keep off any dust which might 

 lodge on it. 



6. As dryness and cleanliness are absolutely essen- 

 tial for success, the legs, and all other parts of the 

 machine, should be continually wiped with warm, dry 

 handkercliiefs, during the interval between the experi- 

 ments. 



7. The rubbers of either machine should be connected, 

 by means of a copper wire, with a gas or water-pipe ; or, 

 in the absence of these, the end of the, wire should be 

 allowed to rest on the floor, so as to keep up a continual 

 production of electricity. In many works, brass chains 

 are recommended; we, however, strongly urge the use 

 of wire, which, being continuous, produces a far better 

 effect than any chain. 



A close observance of the above cautions, &c., will 

 generally ensure successful experiments ; but much de- 

 pends on the state of the weather ; for we have seen the 

 spark of powerful machines, in the best order, reduced 

 to one-fourth its usual length when a change has 

 occurred from an east to a south-west wind. A simpb 

 indication of the state of the atmosphere, as suitable 

 or otherwise for electrical experiments, is to be found 

 by the fur on the back of the cat. If this produces a 

 decided repulsion between the hairs on being rubbed, 

 the electrician may expect success in his attempts with 

 the machine ; but sometimes the air is so loaded with 

 moisture as to render it next to impossible to exhibit 

 any effective results. We have seen more than one 

 eminent lecturer risk his reputation with his audience 

 by attempting electrical experiments in a crowded room. 

 Of course, from ignorance of the cause of failure, the 

 vox populi votes that the experimenter has neglected 

 taking proper precautions. Whilst such may be partly 

 true, our readers will soon become convinced, by ex- 

 perience, that every allowance should be made, under 

 such circumstances, for " the pursuit of science under 

 difficulties." 



We may now proceed to describe machines constructed 

 of resinous materials, which may easily be put together 

 by any of our readers, and in which gutta-percha forms 

 a chief material. Mr. Simmonds, of the west of Eng- 

 land, has exhibited a machine composed of gutta-percha 

 and resin, in the proportion of two of the former to 

 one of the latter substances. In this, the plate (for 

 it was a complete copy of the plate machine), the 

 rubbers, handle, foot supports, and conductor, were all 

 made of the same material ; the points of the conductor 

 were pins ; and it was covered with tinfoil, to make it a 

 good conducting surface. The rubbers were covered 

 with rabbit-skin, and required no amalgam. A machine 

 of this kind, which he favoured us with some six years 

 ago, could be worked in any weather, provided it 

 was first carefully wiped from dust. It seemed to have 

 a very slight attraction for moisture ; and, although the 

 plate was no more than twelve inches in diameter, we 

 have given a shock to twenty persons by means of a 

 Leyden jar, under circumstances in which no glass plate 

 machine could be made to work. If the plate machine, 



