586 



FARMERS' REGISTER 



[No- 11 



be in one o^lass. and cold water in the other, the hot 

 water will be dischar>red ttiucli inoie rapidly than 

 the cold water. The lermentation and deconi po- 

 sition of animal and vegetable subst^ices require a 

 certain degree of heat, which is conc^equently ne- 

 cessary for the preparaiion of the food of plants ; 

 and, a.s evaporation is more rapid in proportion as 

 the temperature is higher, the superfluous parts of 

 the sap are most readily carried off at the time its 

 ascent is quickest. 



Two opinions are current respecting the nature 

 of heat. By one School it is conceived to be 

 a peculiar subtile fluid, of whicii the particles 

 repel each other, but have a strong attraction lor 

 the particles of other matter. By another it is con- 

 sidered as a motion or vibration of the particles of 

 matter, which is supposed to diifer in velocity in 

 different cases, and thus to produce the different 

 degrees of temperature. Whatever decision be 

 ultimately made respecting these opinions, it is 

 certain that there is matter moving in the space 

 between us and the heavenly bodies capable of 

 communicating heat ; the motions of which are 

 rectilinear: thus the solar rays produce heat in 

 acting on the surface of the earth. The experi- 

 ments of Sir W. lierschel have shown that the 

 calorific effects of the solar rays bear no relation 

 to their illuminating powers, the red rays pro- 

 ducing a much greater effect of heat than any of 

 the other colored rays ; and it appears that there 

 are invisible rays distinguished by very different 

 degrees of rcfrangibility, some of which produce 

 heat, and others of which are disiinguislied by their 

 chemical efli'ects. 



The different influence of the different solar rays 

 on vegetation have not yet been studied ; but it is 

 certain that the rays exercise an influence indepen- 

 dent of the heat they produce. Thus plants kept 

 in the dark in a hot-house grow luxuriantly, but 

 they never gain their natural colors ; their leaves 

 arc white or pale, and their juices watery and 

 peculiarly saccharine. 



The earth, when not exposed to the solar rays, 

 is constantly losing heat by radiation, and dif- 

 ferent soils have their temperature differently di- 

 minished by this cause. 



When a piece of sealing-wax is rubbed by a 

 woollen cloth, it gains the power of attracting light 

 bodies, such as leathers or ashes. In this state it 

 is said to he electrical ; and if a metallic cylin- 

 der, placed upon a rod of glass, is brought in con- 

 tact with the sealing-wax, it likewise gains the mo- 

 mentary power of attracting light bodies, so that 

 electricity, like heat, is communicable. When two 

 light bodies receive the same electrical influence, 

 or are electrified by the same body, they repel 

 each other. When one of them is acted on by 

 sealing-wax, and the other by glass that has been 

 rubbed by woollen, they attract each other ; hence 

 it is said that bodies similarly electrified repel 

 each other: and bodies dissimilarly electrified at- 

 tract each other: and the electricity of glass is 

 called vitreous or positive electricity, and that of 

 sealing-wax, resinous or negative electricity. 



When, of two bodies made to rub each other, 

 one is found positively electrified, the other is al- 

 ways found negatively electrified, and, as in the 

 common electrical machine, these states are capa- 

 ble of being communicated to metals placed upon 

 rods or pillars of glass. Electricity is produced like- 

 wise by the contact of bodies ; thus a piece of zinc 



and of silver give a slight electrical shock when 

 they are made to touch each other, and to touch 

 the tongue ; and when a number of plates of cop- 

 per and zinc, 100 lor instance, are arranged in a pile 

 with clothes moistened in salt and water, in the 

 order of zinc, copper, moistened cloth, zinc, cop- 

 per, moistened cloth, and so on, they form an elec- 

 trical battery which will give strong shocks and 

 sparks, and which is possessed of remarkable che- 

 mical powers. The luminous phenomena produced 

 by common electricity are well known. It would 

 he improper to dwell upon them in this place. 

 They are the most impressive effects occasioned by 

 this asent ; and they offer illustrations of lightning 

 and thunder. 



Electrical changes are constantly taking place in 

 nature, on the surface of the earth, and in the at- 

 mosphere; but as yet the effects of this power in 

 vegetation have not been correctly estimated. It 

 has been shown by experiments made by means 

 of the Voltaic battery (the instrument composed of 

 zinc, copper, and water) that compound bodies 

 in general are capable of being decomposed by 

 electrical powers ; and it is probable that the 

 various electrical phenomena occuring in our 

 system must influence both the germination of 

 seeds and the growth of plants. I found that corn 

 sprouted much more rapidly in water positively 

 electrified by the Voltaic instrument than in water 

 negatively electrified; and experiments made upon 

 the atmosphere show that clouds are usually ne- 

 gative ; and as, when a cloud is in one state of 

 electricity, the surface of the earth beneath is 

 brought into the opposite stale, it is probable that 

 in common cases the surface of the earth is positive. 



Different opinions are entertained amongst scien- 

 tific men respecting the nature of electricity. By 

 some the phenomena are conceived to depend 

 upon a single subtile fluid in excess in the bodies 

 said to be positively electrified, in deficiency in the 

 bodies said to be negatively electrified. A second 

 class suppose the effects to be produced by two 

 different fluids, called by them the vitreous fluid 

 and the resinous fluid ; and an hypothesis has 

 been advanced in which they are considered as 

 affections or motions of matter, or an exhibition 

 of attractive powers, similar to (hose which pro- 

 duce chemical combination and decomposition; 

 but usually exerting their action on masses.* 



The power which gives to a bar or needle of 

 steel the property of directing itself to two points 

 of the globe, called north and south poles, depends 

 upon what is called magnetism. It agrees with 

 electricity in many of its laws; but, as far as our 

 researches have hitherto gone, it is most active in 

 its operation on metals and certain of their com- 

 binations. Iron, nickel, and cobalt, are most sus- 

 ceptible of magnetic impressions, and in the harder 

 compounds of iron these impressions produce per- 

 manent effects ; but the recent experiments of M. 

 Arago show, that copper, metals in general, and, 



*In a series of experimptits on the electricity of the 

 atmosphere, made in Malta during the course of seve- 

 ral months, I had ample proof of the truth of the above 

 opinion. Chemical effects were almost constantly 

 taking place, even in serene weather, in a very slight 

 degree. The subject of the experiment was commonly 

 the gelatinous compound of the iodide of potassium 

 and starch ; and almost invariably, excepting occasion- 

 ally in thunder-storms, the iodine was precipitated 

 round the platina wire connected with the earth.— J. D. 



