464 



NATURE 



\SeM. 16, 1880 



as follows : — The two I'ibbons, about afoot long, are both 

 side by side on the table, held at one end between the 

 finger and thumb, and then electrified by drawing along 

 them several times a piece of indiarubber. They are 

 then lifted up from the table, when, if care has been taken 

 that all is warm and dry, they are found no longer to 

 hang straight down side by side, but to stand out and repel 

 each other. 



To obtain an electric spark requires preparations on a 

 larger scale. M. Tissandier recommends the following 

 method : — A piece of stout drawing-paper (warm and dry, 

 of course) is laid upon a table — or upon a warm dry 

 board. It is then rubbed with the dry hand, or with a 

 silk handkerchief, or with a clothes-brush, or, best of all, 

 ■with a piece of indiarubber. It will stick slightly to the 

 table in consequence of its electrification. Now throw 

 down on to it a bunch of keys, and grasping two corners 

 lift up the sheet from the table. If at the very moment 

 of lifting any one holds out his knuckle to the keys he 

 will receive a small pale spark perhaps three-quarters of 

 an inch long. 



A more certain way we have found with what we may 

 call a Tea-tray Elcctrophorus (Fig. 17). A common tea- 

 tray of metal is supported on two dry glass tumblers. A 

 piece of common larown paper ciit so as to be a little 

 smaller than the tray, and with rounded corners, is 

 warmed, laid on the table and rubbed briskly with a piece 

 of indiarubber, or with a clothes-brush. It is then laid 

 down for an instant on the tray and the tray is touched 

 with the hand. The brown paper is then lifted a few 

 inches above the tray. If at this juncture some person 



presents his knuckle to the tray he will receive a bright 

 spark, which under favourable circumstances may be a 

 couple of inches long. By simply putting the paper 

 down, touching the tray, and again lifting up the paper 

 the tray is again charged : and a large number of sparks 

 maybe thus drawn one after the other in rapid succession. 

 The paper may be lifted \>y the hands, but it will be found 

 better if a couple of ribbons or strips of paper be fixed on 

 with wax to serve as handles, as shown in our figure. 



The sparks obtained by the tea-tray elcctrophorus may 

 produce a shght pricking sensation, but to give a regular 

 electric shock will oblige us to store up a charge in a 

 Leyden jar. This important piece of apparatus we have 

 found possible to improvise in the following fashion. A 

 round-bottomed glass tumbler is procured — if of thin 

 glass it is preferable — and is filled to about three-quarters 

 of its height with leaden shot. If shot is not at hand dry 

 coal-dust will answer, but not so well, and great care must 

 be taken to wipe clean the upper part of the tumbler. 

 Everything must be warm and scrupulously dry. Into 

 the shot a silver spcon is stuck to serve the place of 

 a rod and knob. This is held as shown in Fig. 18, by 

 grasping it well in the hollow of the hand, so that the 

 hand may cover the whole of the rounded bottom of the 

 glass. Having thus prepared and grasped our Leyden 

 jar we must charge it with sparks from the tea-tray elec- 

 trophorus. It should be held with the spoon handle near 

 to, but not quite touching the edge of the tea-tray, while 



another person performs the operations of lifting the 

 brown paper up and putting it down, then touching the 

 tray, then lifting up again— and so on until a dozen 

 sparks have been sent into the jar. On touching the 

 knob a smart little shock is experienced in the wrists and 

 elbows, and a short bright snapping spark announces the 

 discharge of the jar. 



The subject of currents of voltaic electricity is some- 

 what beyond the province of " Physics without Apparatus," 

 and so is the greater part of the subject of magnetism. 

 ^Ye may however conclude this article by presenting our 

 readers with a simple mariners' compass described some 

 time ago in a French magazine (Fig. 19). A short knitting- 

 or darning-needle, E, which has been magnetised by rub- 

 bing it on a magnet, is pushed into a small cork, E, and 

 balanced in the following way : — A sewing-needle is fixed, 

 point downwards, in the lower end of the cork, and this 

 is poised on a sewing-thimble. To balance it about the 

 point of the needle a couple of matches pointed at the 

 ends are thrust into the sides of the cork obliquely, and 

 weighted at their lower ends with little balls of sealing- 

 wax. A circle of paper or thin card marked with the 

 " points " of the compass may be attached to the cork ; 

 and to prevent draughts of air from blowing the needle 

 round it should be placed in a deep saucer or dish of 

 glass or porcelain. 



(To he continued.) 



NOTES 



^VE are glad to be able to state that Mrs. Clifford is^to receive 

 a pension from the Civil List in recognition of the eminent 

 services to mathematics of her husband, the late Prof. W. K. 

 Clifford, F.R.S. 



Ln the absence of precise information as to the cause of the 

 lamentable explosion at Seaham Colliery, we cannot say anything 

 useful on the occurrence. When sucli terrible "accidents" 

 occur, Science is invariably asked if she cannot do anything to 

 prevent them, anything to render the miner's occupation less 

 dangerous than it is. Those who ask such questions seem to be 

 ignorant of the fact that, while much remains to be done, science 

 has already done not a little to point out the causes of such 

 explosions and provide the miners with remedies. But it is 

 well known that a large proportion of such explosions are due 

 to the wilful neglect on the part of the miners of the means 

 which science has put into their hands to prevent such calami- 

 ties. We are in a fair ijay of finding out the real nature of the 

 connection between meteorological conditions and explosions in 

 mines ; it is in this direction that investigations should be carried 

 out with thoroughness and zeal. 



The Sir Josiah Mason's Science College, Birmingham, is to 

 be opened on October I next, with an introductory lecture by 

 Prof. Huxley. The classes for students will commence on 

 Tuesday, the 5th. The course of instruction, as at present 

 arranged, includes mathematics, chemistry, physics, and biology. 

 Further details may be learned from our advertising columns. 



Two eminent foreign botanists will, the Gardener's Chronicle 

 states, shortly visit this country — Dr. Asa Gray and M. Alphonse 

 de CandoUe. 



We are glad to learn that the Gilchrist Trustees have given 

 two engineering scholarships to University College, London, to 

 be awarded by competition. There is an entrance scholarship 

 (this year two are offered) of the value of 35/., tenable for two 

 years, to be competed for by those who have not previou,ly been 

 students of the College, and who are not more than eighteen 

 years of age. The examination takes place this year on Sep- 

 tember 2S, and candidates must send in their names to the 

 secretary on or before the 23rd. The subjects of the entrance 

 examinations will be as follows : — Mathematics, n:e:hanics. 



