♦ KNOWLEDGE ♦ 



[Jan. 9, 1885. 



other words, if he desires to make his own apparatus, and 

 to perform his own experiments, he is left, too mucli to his 

 own resources, or to the tender mercies of shopkeepers who 

 want their " shent per shent." 



It is, however, very certain that the expenditure of 

 money upuu " cheap " (and exceedingly nasty) apparatus is 

 a mistike. If economy be a material consideration, far 

 better would it be to become one's own mechanic, or even 

 to purcliase the parts and put them together properly. The 

 necessitous, however, are not the only students who find 

 pleasure or sa'isfaction in constructing apparatus for them- 

 selves, for there is a solid gratification in working experi- 

 ments with home-made instruments. Coupled with this 

 gratification, is the assurance that the individual store of 

 knowledge is being considerably augmented. Home-made 

 apparatus should be, and often is, far .superior to a large 

 proportion of that which is exposed for sale in shop 

 windows. 



These remarks will render apparent my reason for 

 undertaking this series of papers, iu which it will be my 

 object to enable my readers to make such apparatus as may 

 hi necessary to explain the various laws and applications 

 of electricity, and to aflTord to the amateur a source of 

 pleasurable employment not altogether devoid of intel- 

 lectual profit. Points of theory will, as far as practicable, 

 be eschewed. The plan will rather be to euuuciate the 

 laws generally accepted, and then to describe systematically 

 the manufacture and application of such apparatus as may 

 help to explain or verify the law. In order to render the 

 work as complete iu itself as pos.sible, I purpose commencing 

 with the more rudimentary portions of the subject, and 

 then by following out a specie.^ of evolution in electrical 

 instrument making, to attempt ultimately some of the most 

 delicate and, withal, the most interesting pieces of appa- 

 ratus conceivable. 



It is only by practical experience that we become ac- 

 quainted with the various little details in construction 

 e.ssential to tlie good and reliable working of the apparatus. 

 To work well, apparatus should be made well, and we 

 might just as feasibly expect a wooden horse to carry a 

 man across the country as to expect a clumsily or care- 

 iessly-made piece of apparatus to behave as an orderly and 

 well-conducted piece of machinery should do. 



There are doubtless some parts of various instruments 

 which the majority of amateurs could hardly hope to 

 succeed in njakicg. Tlii.s, however, need not prevent 

 them making all that it is possible for them to do, but 

 when they find it necessary to call upon profe.ssional skiU, 

 let them be sure that they get it ; and this they can only 

 rely u])on by going to a good establishment. 



Befoi-e the student is able to prepare any experiments, 

 it is necessary that he should provide himself with a few 

 tools and sundries which be will require more or less 

 frequently. Let us first, then, decide upon a small stock- 

 in-trade, and in doing so, let us bear in mind that we are 

 preparing for a series of experiments in the department of 

 " frictional " or " static " electricity. 



Ex. I. — One of the first necessities is an insulating 

 varnish. This may be prepared in a small necked, stoppered 

 glnss bottle of about 12 oz. capacity. Into this put about 

 half-a-pint of methylated spirit, and in that dissolve shellac 

 (previously broken into small )iieces) until it assumes a 

 consistency similar to that of ordinary commercial gum. 

 Shellac is an exceedingly useful material, and a quantity of 

 it, say a pound, should be kept on hand. The solution 

 of the lac takes a day or two. When water is used 

 as a solvent (not that water is applicable in this particular 

 case), we may, generally speaking, increase the rate of solu- 

 tion by applying heat ; but the spirit is too volatile for this 



to be done, and we must therefore be satisfied with such 

 speed as we may get. When thus prepared, it is carefully 

 stoppered and put away in a cool place to be called upon 

 when required. It is sometimes said that the varnish will 

 not keep, and that the spirit will evaporate; but I have 

 some by me which I made two or three years ago, and 

 which is as good now as when it was first made. Every- 

 thing depends on the stopper. If it fits well it will prevent 

 evaporation, and the partial solidification of the little varnish 

 that happens to find its way into the neck should make 

 good any shortcoming on the part of the stopper. A glass 

 stopper is preferable to a cork, because the latter would 

 very speedily get fixed irreuiovably. Shellac varnish 

 answers best when used thin. If too thick the outer film 

 is deprived of its spirit, and becomes practically solid 

 before the spirit associated with the subjacent lac has had 

 time to evaporate. Consequently a very long time is likely 

 to elapse before the insulating coating becomes thoroughly 

 dry and set. When a coating of considerable thickness is 

 required, it is much the better plan to apply a succession of 

 thin layers, allowing each one to dry before the succeeding 

 one is applied. A little vermilion added to the varnish 

 imparts a beautiful glossy colour, and such a varnish is far 

 preferable to ordinary sealing-wax varnish, being so much 

 purer. Shellac varnish is applied by a brush, which so long 

 as it is kept clean may be allowed to dry after having been 

 used. Immersion in the solution for half an hour or so 

 will restore its pliability. 



Ex. II. — Another insulator frequently required is paraffin- 

 wax. This is a white, solid substance, to be by no means 

 confused with paraffin-oil. W^hen used, it is applied in the 

 liquid state, and allowed to cool, which it does very speedily. 

 As it is volatile, it is best not to raise it to too high a tem- 

 perature when melting. The melting is generally accom- 

 plished by heating the wax in a small tin box, or even a 

 saucer, over a spirit or Buusen flame. 



Substances to bo coated with paiaffiu require, generally 

 speaking, to be immersed in the molten wax. Sometimes 

 a difl'erent course is pursued, but reference will be made to 

 this when occasion requires. 



Ex. III. — As a solid suspending insulator, nothing is 

 superior to silk fibre, a small quantity of which will prove 

 useful. Silk-thread and narrow silk-ribbon will also be 

 requisitioned occasionally. The colour is practically 

 immaterial. 



Ex. IV. — Glass is, of all insulat..irs, the one most 

 generally employed when strength is a necessary quality ; 

 and half a pound of quarter-inch and a like quantity of 

 half-inch tubing will be certain to prove useful. " Com- 

 bustion," or hard flint glass, tubing (pale green in colour) 

 is preferable to the soft tubing for straight insulators ; 

 but, where they are to be bent, the softer kind must, 

 generally speaking, be resorted to. A small quantity of 

 glass rod, quarter to half an inch iu diameter, will also 

 prove useful. 



(To he continiicil.) 



Patents. — The number of applicants for Letters Patent during 

 the year just ended amounted to 17,110. 



Bankruptcies is 1881. — NotwitVistanding tlie fact that the past 

 year has been one of universal depression, the dccrcaso in the 

 number of bankruptcies has been most remarkable. In 1S83 the 

 number ^a^-etted for England and Wales was 10,183 ; last year there 

 were only 3,721 persons declared bankrupt, or barely a third of the 

 number of the previous year. In this statement of ntlaiis there 

 must be much that stands to the credit of the new Bankruptcy Act, 

 for everything else has favoured an increase of bankruptcies. 

 Whatever room there may be for improvement in details, it is very 

 obvious that the new Bankruptcy Act is a success. 



