^8 • KEPOBT 1861. 



1. The unit of electromotive force, or tension, or potential. 



2. The unit of absolute electrical quantity, or of static electricity. 



3. The unit of electrical cm-rent, which should be foi-med by the combination of 

 the imit of quantity with time. Such, for example, as the flow of a unit of elec- 

 tricity per second. 



4. The tmit of electrical resistance, which should be the same unit as that of 

 cmTent, viz. a wire which would conduct a imit of electi-icity iu a second of time. 



The necessity of the adoption of some nomenclature was also pointed out, in 

 order to adapt the system to the wants of practical telegraphists. 



On the Deposit of Metals from the Negative Terminal of an Induction Coil 

 during the Electrical Discharge in Vacuo. By J. P. Gtassiot, F.B.8. 



When the electric discharges by an induction coil are made from platinum ^vires 

 hermetically sealed in a vacuxmi tube as usually constiiicted, the wire which is 

 attached to the negative terminal of the coil shortly assmnes the appearance of 

 being con-oded : this arises from veiy minute particles of the metal having been 

 disintegi-ated and separated fi'om the wii-e, which particles are deposited or. the 

 eides of the tube in a lateral dii'ection. K the vnres are protected within the va- 

 cuum by being covered with glass tubing open at the end, but extending about one- 

 eighth of an inch beyond the wii-e, it is the iaside of this tubing that becomes coated 

 with metal : but, exclusive of this lateral action, a portion of the negative discharge 

 will be obsei-ved to obti-ude from the glass tubing iu the fonn of a limiinous brush j 

 this luminosity is very sensibly aflected by a magnet, and can in this manner be 

 made to impinge on difl'erent parts of the vacuiun tube, and wherever it is thus 

 impinged heat is always evolved. The above phenomenon of the deflection of the 

 negative discharge was described in a paper commimicated by me to the Eoyal 

 Society; and as I was subsequently desirous to examine with greater accuracy the 

 nature* of the deposit thus obtained from the negative tenninal, and pai-ticularly if it 

 coidd be obtained in the same manner fi-om other metals than platinum, I had an ap- 

 pai-atus constructed in which the discharge coidd be dii-ected on slips of glass : the 

 apparatus was also so constructed that wu-es of difl'erent metals could be inserted, 

 and in this manner I succeeded in obtaining deposits of the following metals, gold, 

 silver, copper, platinum, zinc, iron, tin, lead (brass), magnesiiun, tellm-iimi, bis- 

 muth, cadmium, and antimony : for many of these I was indebted to Mr.Matthiessen, 

 who fm-nished them to me in a pm-e state. With gold, silver, platinum, tin, and. 

 bismuth, the deposit would take place in the state as now exhibited in about twenty- 

 four hom-s' action ; if the discharges were continued, the deposit became denser ; 

 and, as will be observed, in one or two instances the centre is crystalline. With 

 reflected light a large sm-face exhibits the lusti-e of the metal ; with ti-ansmitted 

 light the outer portion is transpai'ent, sho'wTng the peculiar colom* of the metals — as 

 gold, gi-een; silver, bluish purole; platinum and tin, blackish grey. Telluriimi, with, 

 the exception of antimonj^, I found disintegi-ated more freely than the other metals, 

 while ii-on and magnesiimi were the most diflicidt; the deposit of the latter is 

 scarcely perceptible. With aluminiimi wires I could not obtain any deposit after 

 forty-eight hoiu-s' constant action ; on one occasion I observed a faint ti-ace on the 

 glass, but in repeating the experiment ^vith another wire no sign of any deposit coidd 

 be obtained. Under the microscope the thin layer or deposit of metal is not resolved 

 into any fonn, but appears as a mere film on the sm-face of the glass. From a brass 

 ■ware tenninal there was not any separation of the original metak. I had a tube 

 consti-ucted with two wires, both protected by glass tubing ; a long slip of glass was 

 inserted, so that the discharges fi-om the + and the — temiinals of the coU could 

 be made with protected wii-es imder the same conditions. The wii-es were of gold. 

 The usual deposit took place at the negative ; but after twenty-four hom-s' constant 

 action not the slightest indication of any deposit fi-om the + wire coidd be obsen-ed. 

 With antimony a veiy peculiar eflect was obtained: instead of the metal being 

 deposited in a cii-cular foi-m, it spread nearly all over the glass and on the sides of 

 the vacuum tube. I repeated the experiment by inserting slips of glass of suflicient 

 length to reach beyond the tenninals. Two of these glasses are on the table, and,' 

 if examined, it will be seen that the + discharge has apparently repelled the deposit 

 as it formed fi-om the negative wii-e, leaving- the space somewhat analogous to the* 



