VOL 



art- brought into contaft, a brilliant fpark is produced, and 

 the wires ftick together with conliderable force, as if they 

 were welded, or united by fufion. If the parts in contaft 

 be held with the fingers, a confiderable heat will be per- 

 ceived, which will be greater as the battery is more power- 

 ful, and jnverfely as the thicknefs of the wires. 



Small wires feem to affect the eleftric fluid in a manner 

 fimilai' to that in which light is affefted by a convex lens, 

 or a concave mirror, by concentrating and compelling a 

 large quantity of cledlricity to pafs through a fmall channel. 

 This appears to be the cafe with common eleftricity, as well 

 as galvanifm, lince by difcharging the eleftrical battery 

 through very fmall wires, the metals become fufed and 

 oxydated. 



On the galvanic battery this experiment (hould be made 

 as follows : at each end of the battery fhould be placed a 

 rod of metal, with a clean ball at the top of each. Between 

 the two balls muft be ftretched a piece of very fmall wire, not 

 exceeding TTirth of an inch in diameter, while the circuit 

 is interrupted in fome other part of the battery. As foon 

 as the wire is fixed, the circuit mufl be completed where it 

 was broken, and the current will inllantly be determined 

 through the fmall wire, which will in confequence become 

 ignited. 



It was difcovered by Dr. Wollafton, that, in the ignition 

 of wire by the voltaic battery, there was one certain diame- 

 ter of the wire, in which the length ignited was the greateft, 

 above or below which the length was lefs. This does not 

 arife from more heat being fent through the wire in which 

 the greated length was ignited, but from the ratio of the fur- 

 face of the very fmall wire being fo much greater to its foli- 

 dity than in thicker wire, by which a greater proportion of 

 heat is carried ofl by radiation ; but when the diameter is 

 beyond a certain extent, then a lefs length is ignited, from 

 the heat being lefs concentrated. 



It has alfo been found, that very different lengths of wire 

 are heated of different metals when their diameters are equal. 

 This appears to take place from the relative coaiduftive 

 powers of the different metals for elcftricity, which appears 

 to be as their conducing powers for heat. Platina, being the 

 worft condudtor, has a greater length heated ; and filver, 

 which is known to be a good conduftor, has a lefs length 

 heated. 



If the battery be very powerful, it will be fufed and oxy- 

 dated. When a connexion is formed between the two ends 

 of the battery, by means of the very thin foils of metals, 

 fuch as leaf-gold, the metals undergo brilliant combullion, 

 exhibiting different coloured flames. Charcoal and plum- 

 bago, prefented by Iharp angles, are fimilarly deflagrated. 

 If the ends of the two wires coming from the battery be 

 made to touch each fide of a fmall globule of mercury, the 

 latter will inflame with a bright flalh. This lieat, furnilhed in 

 the'galvanic current, is alfo very apparent while it is paffing 

 through moifl conductors. Different fluids fubjefted to de- 

 compofition in the circuit, in glafs tubes, become confider- 

 ably heated, and this will be found the cafe, as the diameter 

 of the tube is lefs. 



Sir H. Davy attributes this heat to the decompofition, 

 which muft ftrikc any one as being an error. Heat we al- 

 ways find to be evolved during combination ; the very re- 

 vfrfe of which ought to take place during decompofition. 



ABwn of Galvanifm upon Animals All animal fub- 



ftances, either dead or living, if not deprived of their moif- 

 ture, are tolerably humid conductors of Galvanifm. In the 

 living fubjeft, independent of its conducing power, it has 

 the property of being affecled in a peculiar manner. All 

 thofe animals which poilefs excitability are aifcfted by Gal- 



VOL 



vanifm as they would be affeftrd by any other violent lli- 

 niulus ; and if the excitable part be at all mufcular, the 

 fibres are vigoroufly contraded. This caufes, in a living 

 and confcious animal, a fenfation not unlike an c-leftric 

 fhock. The fliock is more hke that of common eleftricitf , 

 as the plates of the battery are fmaller and more numerous. 

 When the plates are of very large furface; z fort of vibra- 

 tory motion is felt through the part attended with a fenfa- 

 tion of heat ; and this, in a powerful battery, is felt fo 

 long as the connexion is kept up. The befl; mode of taking 

 the fliock is firil to moiif en the hands, or the part where the 

 effeft is to be applied ; grafp in each hand a piece of metal, 

 fuch as two fpoons, and touch each end of the battery with 

 the other ends of the fpoons at the fame time. If it is in- 

 tended to be applied to any other part, let two plates, of 

 about two inches in diameter, be each attached to the wires 

 coming from the battery, and let the plates be applied to fome 

 two parts : if the effeft be too fevere, let fome inferior con- 

 duAor be placed between the plate and the fkin. 



Sir H. Davy found, that when an animal fubftance was 

 placed in the circuit of a galvanic battery, the different com- 

 pounds contained in it were decompofed. This was more 

 efpecially the cafe with the faline bodies contained in the ani- 

 mal fluids ; the acids of the falts were found on the pofitive 

 fide of the battery, and the bafesof the falts on the negative. 

 Should it be afcertained that any redundancy of faline mat- 

 ter is the caufe of difeafe, Galvanifm might be employed 

 with great fucccfs in feparating thofe bodies from the fylleni. 



Dr. Wollafton has given fome hints in Nicholfon's Jour- 

 nal, from which it appears probable that the power of the 

 glands in fecreting difi"erent fluids is dependent upon the 

 eleftrical itate of the glands ; by which they are induced to 

 attraft all bodies in a contrary ftate to themfelves. The opi- 

 nion of this ingenious gentleman has been llrongly corrobo- 

 rated by fome experiments made by Meflrs. Home and 

 Brandt. Phil. Tranf. 



Thefe, however, are fpeculations on which we cannot at 

 prefent place ilrift reliance. The fame conjefture which is 

 apphed to fecretion may be applied to the oxygenation, or 

 rather the decarbonization of the blood in the lungs ; fincc 

 the carbon appears to be transferred through the membranes 

 between the pulmonary arteries jnd the interior of the lungs. 

 The fame theory may be alfo' aujilied to account for the 

 change of the colour of the bloocl between the foetus and the 

 mother. Mufcular excitabihty may perhaps arife from a 

 certain eledtric Hate of the mufcular fibre caufed and kept 

 up by the arterial blood ; and if we may be allowed to carry 

 the conjecture ilill further, mufcular motion may perhaps 

 be caufed by the relative eleftric ftates of the mufcles, and 

 the brain and nerves. 



VOLTANA, in Geography, a town of Spain, in Ara- 

 gon ; 5 miles N.W. of Ainfa. 



VOLTARE, Ital. in Mufic-books, to turn over; whence 

 volti, turn, volti fubito, turn quick, and often only the ini- 

 tials of thefe words V.S. Si -volti, at the end of a move- 

 ment, denote, the leaf is to be turned over to another move- 

 ment. And, in courtcfy, it is fometimes faid, volti fe piace, 

 turn over if you pleafe. 



VOLTE, in the Manege, fignifies a round or circular 

 motion, confifling of a gait of two treads, m.adc by a horfe 

 going fideways round a centre : the two treads making 

 parallel tracks, one by the fore-feet, larger, and the other 

 by the hind-feet, fmaller ; the flioulder bearing outwards, 

 and the croup approaching towards the centre. 



Volte, Dt-mi, is a half-round of one tread, or two, 



made by the horfe at one of tlie angles, or corners, of the 



volte, or at the end of the line of the paiTade j fo as when 



3 O 2 he 



