Sept, 18, 1885.] 



♦ KNO\A/LEDGE 



249 



strips of tinfoil five inches long and an inch wide. Cover 

 one face of each for four inches of its length with flour 

 paste and therewith attach them to the inner surface of 

 the jar, placing them four inches up the glass and as 

 nearly as possible opposite each other or at the extremities 

 of a single diameter, and leaving an inch of foil in each 

 case free. Subsequently bend these free ends over the 

 bottom edge and paste on the outside of the glass. Then 

 procure a piece of copper, bras.s, or even iron wire, of any 

 convenient thickness, pass it round the outside of the 

 jar three-quarters of an inch from the bottom, twist the 

 two ends tightly together (so as to prevent subsequent 

 slipping), and bend the twisted ends in a hook as at C 

 (Fig. 61). This hook affords a me.-ins of attachment for 

 a light chain, wire or any other substance which may be 

 used for an earth connection. The wire should make 

 electrical contact with the tin-foil strips. 



To return to the stopper. The hole is usually fitted 

 with a piece of glass tubing, through which the metal 

 wire W W is passed and held in position by binding it 

 round with sufficient silk ribbon to make a tight 

 fit ; but I scarcely think this is necessary, more 

 particularly if the instrument is kept clean and 

 free from dust. Let us simply use a piece of wire 

 or rod six inches long, and fitting friction-tight into 

 the hole in the wood. This is thicker than is really 



Fig 61 



Fig 63 



necessary, a much thinner piece of wire answering in 

 most cases equally well ; but the cost would not be more 

 than a penny, and it would allow us to place a mode- 

 rately heavy body on the plate A without any fear of the 

 whole thing collapsing. After seeing to the fit remove 

 it from tlie wood, and with a second-cut file work a small 

 length (an eighth of an inch) down to about half the 

 original diameter— that is, to :iii ii'l'-IiIIi ''f im inch. Thi.s 

 may be done by securing the nul m n mu;iII liand-vicc 

 (Ex. XXVTIT) which is placrd in ll,,' hft l,;uul. Tluii, 

 laying the eii.l of the rod on thr laMr, jkixs tl,r lil,. (lul.l 

 in the right li;nM)..v,r If, (i.niin- il :it thr sm4,„' tim,. 

 towards the lilr. At tl..' sunir linir an cvru shouKlrr 

 CD, Fig. t;:',, .slu.ul.l 1.0 f.a-iiHMl. Xrxt iKnunur Ai<^^n 

 the end A to about tlie shajio shown, making the extreme 

 edge not less than half-an-inch wide. If the rod is of 

 iron it will require to be made red-hot before it is ham- 

 mered down. 



The jilate A, Fig. 61, may be cut from tinned iron, but, 

 of course, brass looks nicer, is more substantial, and will 



fit better on to the rod. Cut a piece of metal (say a thirty- 

 second of an inch thick) as nearly circular as possible, 

 making the diameter 3 or 31 in. ' Use a smooth file for 

 finishing-off, and avoid leaving any points or other 

 projections. Drill through the centre (Ex. XXIX. to 

 XXXV.) a hole an eighth of an inch in diameter. 

 Through this, pass the reduced end B of the rod A B, Fig. 

 63, and rivet together by hammering out the projecting 

 portion B. See that A rests fairly on the .shoulder C D, 

 so as to avoid any danger of the jJate tilting over at any 

 time. If it is necessary — that is, if sufficient rigidity is not 

 obtained, the two may be soldered together. (Ex. XI. to 

 XIV.) Before fitting the plate, the rod must be passed 

 through the wooden stoppei' again. 



The next thing is to attach the leaves L L. These 

 maybe of Dutch metal, of which a whole book may be 

 purchased for a few pence. Place a leaf (lifting it with 

 the point of a clean knife-blade; between two pieces of 

 note-paper, lay on a board, and cut two strips 3 in. or so 

 long and h in. wide. Remove carefully the upper strips 

 of paper, and, having already gummed the two flat faces 

 on A (Fig. 63), lay one on the end of one of the metal 

 strips, raise cleanly and carefully, and place the other 

 face on one end of the other metal strip. If properly 

 done the two leaves or strips will hang evenly and 

 parallel. Above all, draughts should be avoided, and the 

 fingers should be kept from coming into contact with the 

 leaves. If any accident happens it is useless attempting 

 to put matters right. The only resource is to cut another 

 strip, or two if need be. 



When the strips are in position, hold the rod vertically, 

 pass the lower portion together with the strips into the 

 jar, and fix the stopper, D, into the neck. Let W W 

 (that is A B, Fig. 63), remain about 3 inches above the 

 stopper. Then having prepared some sealing-wax or 

 shellac varnish, brush a little over the stopper, sealing up 

 any space that may be left in the central hole through 

 which the rod passes, or any interstices that may present 

 themselves between the stopper and the glass. A little 

 ordinary sealing-wax may be used in the ordinary way 

 with perhaps equal advantage, but it does not always 

 look so neat as might be desired. 



The young electrician will now be provided witli a 

 very efficient instrument, and I think it may fairly be 

 said that the cost of the parts does not exceeded three- 

 pence, especially if only an irou rod and a tinned iron 

 plate are used. Sometimes I have been driven into a 

 hole for want of an electroscope. I have then extem- 

 porised one for the occasion with very satisfactory 

 results ; but of this a few words next time. 



SCRAPS FROM THE BRITISH 

 ASSOCIATIOX. 



THOUGH the accumulation of farts is iiidisi-fn, 

 to tllegn.^^th ,.f srinu-r. a iliMi-aial fa.-i. ; , 



111 IT 



J so! 



Mcwe.i as me dust of science. The dust which floats in 

 the atiiiis]ilierc is to the common observer mere inco- 

 liercut matter in a wrong place, while to the man of 

 science it is all important when the rays of heat and 

 light act upon its floating particles. It is by them that 

 clouds and rains are influenced; it is by their siKctivc 

 influence on the solar waves that the blue of the heavens 

 and the beauteous colours of the sky glorify all nature. 

 So, also, ascertained through isolated facts, forming the 



